diff --git a/conductor/tracks/metadata_field_cache_20260624/metadata.json b/conductor/tracks/metadata_field_cache_20260624/metadata.json
new file mode 100644
index 00000000..142b22c6
--- /dev/null
+++ b/conductor/tracks/metadata_field_cache_20260624/metadata.json
@@ -0,0 +1,68 @@
+{
+  "track_id": "metadata_field_cache_20260624",
+  "name": "Child 3: Metadata Field Cache",
+  "track_type": "campaign_child",
+  "parent_campaign": "metadata_ssdl_defusing_20260624",
+  "created_date": "2026-06-24",
+  "branch": "master",
+  "depends_on": ["code_path_audit_20260607", "metadata_nil_sentinel_20260624", "metadata_generational_handle_20260624"],
+  "blocks_within_campaign": [],
+  "scope": {
+    "new_files": [
+      "conductor/tracks/metadata_field_cache_20260624/spec.md",
+      "conductor/tracks/metadata_field_cache_20260624/plan.md",
+      "conductor/tracks/metadata_field_cache_20260624/metadata.json",
+      "conductor/tracks/metadata_field_cache_20260624/state.toml",
+      "tests/test_metadata_field_cache.py",
+      "docs/reports/TRACK_COMPLETION_metadata_field_cache_20260624.md"
+    ],
+    "modified_files": [
+      "src/aggregate.py (MetadataFieldCache + field-access migrations)",
+      "src/ai_client.py (field-access migrations; specific files TBD by Tier 2)",
+      "conductor/tracks.md",
+      "docs/reports/campaign_measurements_20260624.md"
+    ],
+    "deleted_files": []
+  },
+  "estimated_effort": {
+    "method": "scope (per workflow.md §Tier 1 Track Initialization Rules). NO day estimates.",
+    "phase_1": "1 task: 4 behavioral tests",
+    "phase_2": "1 task: MetadataFieldCache + 123 field-access site migrations",
+    "phase_3": "1 task: 6 VCs + budget gate + TRACK_COMPLETION + state + tracks.md + campaign SHIPPED"
+  },
+  "verification_criteria": [
+    "VC1: MetadataFieldCache exists",
+    "VC2: Production code uses the cache at field-access sites",
+    "VC3: Behavioral test exists and passes",
+    "VC4: Budget gate met (drop >= 30% vs post-child-2 measurement)",
+    "VC5: Full test suite remains green (11/11 tiers PASS)",
+    "VC6: 4 audit gates remain clean"
+  ],
+  "known_issues": [],
+  "deferred_to_followup_tracks": [],
+  "regressions_and_pre_existing_failures": [],
+  "pre_existing_failures_remaining": [],
+  "risk_register": [
+    {
+      "id": "risk-1",
+      "description": "Cache invalidation is wrong (stale values returned)",
+      "likelihood": "medium",
+      "impact": "Production code returns stale Metadata values",
+      "mitigation": "Cache keyed by handle; when underlying value changes, handle's generation bumps (via registry), invalidating cache entries"
+    },
+    {
+      "id": "risk-2",
+      "description": "The 123 field-access sites are not actually 123 (audit was wrong)",
+      "likelihood": "low",
+      "impact": "Migration scope unclear; budget gate measurement is invalid",
+      "mitigation": "Re-run detect_access_pattern_evidence after migration to count actual sites"
+    },
+    {
+      "id": "risk-3",
+      "description": "Budget gate fails (drop < 30%)",
+      "likelihood": "low",
+      "impact": "Child 3 cannot ship; campaign pauses",
+      "mitigation": "Cache collapses 123 lookups to 1 lookup each; expected large drop"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/conductor/tracks/metadata_field_cache_20260624/plan.md b/conductor/tracks/metadata_field_cache_20260624/plan.md
new file mode 100644
index 00000000..b39df841
--- /dev/null
+++ b/conductor/tracks/metadata_field_cache_20260624/plan.md
@@ -0,0 +1,86 @@
+# Plan: metadata_field_cache_20260624
+
+3 tasks, 3 atomic commits. Same pattern as children 1 and 2.
+
+## Phase 1: Behavioral Test (1 task)
+
+- [ ] Task 1.1: Write `tests/test_metadata_field_cache.py`.
+  - WHERE: New file `tests/test_metadata_field_cache.py`
+  - WHAT: 4 tests (per spec FR3)
+  - HOW: Use 1-space indentation
+  - SAFETY: Test imports `MetadataFieldCache` + `MetadataHandle` from their production locations
+  - COMMIT: `test(metadata): behavioral test for field cache (MetadataFieldCache)`
+  - GIT NOTE: 4 tests; will be RED until Phase 2 ships
+  - VERIFY: `uv run pytest tests/test_metadata_field_cache.py -v` shows 4/4 FAIL (expected)
+
+## Phase 2: Implementation (1 task)
+
+- [ ] Task 2.1: Add `MetadataFieldCache` + migrate the 123 field-access sites.
+  - WHERE: `src/aggregate.py` (cache type) + the 123 field-access sites across `src/`
+  - WHAT:
+    - Add `class MetadataFieldCache` with `get`, `set`, `invalidate` methods
+    - Migrate the 123 `entry.get('key', default)` and `entry['key']` sites to use the cache
+  - HOW: Use `manual-slop_py_add_def` for the cache type; `manual-slop_edit_file` for the migration sites
+  - SAFETY: Verify with `ast.parse`; run the 4 tests + the child-1 + child-2 tests + the 14 previously-failing tests
+  - COMMIT: `feat(metadata): MetadataFieldCache + 123 field-access site migrations`
+  - GIT NOTE: 123 sites now use cache; cache invalidation on generation bump (child 2's registry)
+  - VERIFY: `uv run pytest tests/test_metadata_field_cache.py tests/test_metadata_generational_handle.py tests/test_metadata_nil_sentinel.py -v` shows all PASS
+
+## Phase 3: Verification + Budget Gate (1 task)
+
+- [ ] Task 3.1: Run all 6 VCs; capture the budget gate measurement; write end-of-campaign TRACK_COMPLETION.
+  - WHERE: All audit gates + test suite + SSDL measurement + campaign umbrella
+  - WHAT:
+    - Run VC1-VC6 for the child
+    - Compute the new effective-codepaths number
+    - Compare to post-child-2 measurement; require drop ≥ 30%
+    - Write the child's TRACK_COMPLETION report
+    - Update this track's `state.toml` to `status = "completed"`, all 3 phases completed
+    - Append to campaign_measurements_20260624.md
+    - Update conductor/tracks.md
+    - ALSO: write the campaign's end-of-campaign TRACK_COMPLETION at `docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md`
+    - Update the campaign umbrella's `state.toml` to `status = "completed"`, all 4 phases completed
+  - HOW: Run each VC command, capture output, write the report.
+  - SAFETY: Same as children 1 and 2
+  - COMMIT: 3 child commits (state, TRACK_COMPLETION, tracks.md) + 3 campaign commits (state, TRACK_COMPLETION, tracks.md)
+  - GIT NOTE: Per workflow.md
+  - VERIFY: All 6 VCs pass; budget gate met; campaign umbrella SHIPPED
+
+## Commit Log (Expected)
+
+1. `test(metadata): behavioral test for field cache` (Task 1.1)
+2. `feat(metadata): MetadataFieldCache + 123 field-access site migrations` (Task 2.1)
+3. `conductor(state): metadata_field_cache_20260624 SHIPPED` (Task 3.1)
+4. `docs(reports): TRACK_COMPLETION for metadata_field_cache_20260624` (Task 3.1)
+5. `conductor(tracks): add metadata_field_cache_20260624 row` (Task 3.1)
+6. `docs(reports): TRACK_COMPLETION for metadata_ssdl_defusing_20260624` (Task 3.1)
+7. `conductor(state): metadata_ssdl_defusing_20260624 SHIPPED` (Task 3.1)
+8. `conductor(tracks): add metadata_ssdl_defusing_20260624 row + 3 child rows` (Task 3.1)
+
+## Verification Commands
+
+```bash
+# VC1: cache type exists
+grep -rn "class MetadataFieldCache" src/
+
+# VC2: production uses cache
+grep -rn "field_cache.get\|field_cache.set" src/
+
+# VC3: tests pass
+uv run pytest tests/test_metadata_field_cache.py -v
+
+# VC4: budget gate (final measurement)
+uv run python -c "from src.code_path_audit_ssdl import compute_effective_codepaths; ...; print(compute_effective_codepaths(metadata_profile, 'src'))"
+
+# VC5: full test suite
+uv run python scripts/run_tests_batched.py
+
+# VC6: 4 audit gates
+uv run python scripts/audit_weak_types.py --strict
+uv run python scripts/generate_type_registry.py --check
+uv run python scripts/audit_main_thread_imports.py
+uv run python scripts/audit_no_models_config_io.py
+
+# Campaign-wide
+cat docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md
+```
\ No newline at end of file
diff --git a/conductor/tracks/metadata_field_cache_20260624/spec.md b/conductor/tracks/metadata_field_cache_20260624/spec.md
new file mode 100644
index 00000000..5dcbb0ad
--- /dev/null
+++ b/conductor/tracks/metadata_field_cache_20260624/spec.md
@@ -0,0 +1,114 @@
+# Track Specification: metadata_field_cache_20260624
+
+## Overview
+
+Child 3 of the `metadata_ssdl_defusing_20260624` campaign. Introduces `MetadataFieldCache` keyed by `(handle.index, field_name)`. The 123 string-keyed `entry.get('key', default)` field-access sites become 123 cache lookups. **BLOCKED_BY child 2** (the handle provides the stable cache key).
+
+## Current State Audit (master @ child-2-SHIPPED, after metadata_generational_handle_20260624)
+
+- `NIL_METADATA` sentinel exists (from child 1)
+- `MetadataHandle` + `MetadataHandleRegistry` exist (from child 2)
+- The 123 field-access sites in `src/aggregate.py`, `src/ai_client.py`, and other production files use `entry.get('key', default)` or `entry['key']` patterns
+
+## Goals
+
+| ID | Goal | Acceptance |
+|---|---|---|
+| G1 | `MetadataFieldCache` introduced: keyed by `(handle.index, field_name)` | The cache type is exported; can be created, queried, and invalidated |
+| G2 | The 123 field-access sites use the cache | `grep -rn "MetadataFieldCache\|field_cache.get\|field_cache.set" src/` returns ≥ 1 hit per site |
+| G3 | 1 behavioral test for the cache | `tests/test_metadata_field_cache.py` exists; asserts hit, miss, invalidation via generation bump |
+| G4 | Budget gate met: effective-codepaths drop ≥ 30% vs post-child-2 measurement | Re-measurement shows the drop |
+
+## Non-Goals
+
+- Touching the 4 other `dict[str, Any]` aliases — out of scope
+- Touching the list-typed aggregates — out of scope
+- Replacing the 3 candidate placeholders — blocked on `any_type_componentization_20260621`
+- Cache for the inner Metadata values within nested structures (the campaign handles the top-level Metadata)
+- Eviction policy (LRU, etc.) — the cache is small (123 entries) and keyed by handle; no eviction needed
+
+## Functional Requirements
+
+### FR1: Cache type
+
+In a sensible location (likely `src/aggregate.py`):
+
+```python
+class MetadataFieldCache:
+    def __init__(self) -> None:
+        self._cache: dict[tuple[int, str], Any] = {}
+        self._generations: dict[int, int] = {}  # mirrors the registry
+    
+    def get(self, handle: MetadataHandle, field_name: str) -> Any:
+        # if handle.generation != self._generations[handle.index], return None (sentinel equivalent)
+        # otherwise return self._cache.get((handle.index, field_name), NIL)
+    
+    def set(self, handle: MetadataHandle, field_name: str, value: Any) -> None:
+        # if handle.generation != self._generations[handle.index], ignore (stale write)
+        # otherwise self._cache[(handle.index, field_name)] = value
+    
+    def invalidate(self, index: int) -> None:
+        # clear all entries for this index; bump generation
+```
+
+(Exact API up to Tier 2; the contract is: cache keyed by `(index, field_name)`, generation-aware invalidation.)
+
+### FR2: Migrate the 123 field-access sites
+
+For each `entry.get('key', default)` or `entry['key']` site in the production code:
+- Replace with `cache.get(handle, 'key') or NIL_METADATA.get('key', default)` (or similar; the exact pattern depends on whether the cache returns the raw value or the cached Metadata)
+- Alternative: the cache stores the entire Metadata (or per-field values), and consumers request `(handle, 'field_name')`
+
+The exact migration pattern is up to Tier 2. The acceptance criterion is that the 123 sites are migrated.
+
+### FR3: Behavioral test
+
+`tests/test_metadata_field_cache.py` with at least 4 tests:
+- `test_cache_hit`: `cache.get(handle, 'key')` after `cache.set(handle, 'key', value)` returns value
+- `test_cache_miss`: `cache.get(handle, 'key')` without prior set returns NIL (or None)
+- `test_cache_invalidation_on_bump`: after `cache.invalidate(handle.index)`, `cache.get(handle, 'key')` returns NIL
+- `test_cache_stale_write_ignored`: `cache.set(stale_handle, 'key', value)` does not write
+
+## Non-Functional Requirements
+
+- NFR1: 1-space indentation
+- NFR2: CRLF line endings on Windows
+- NFR3: No comments in source code
+- NFR4: Per-task atomic commits with git notes
+- NFR5: No new pip dependencies
+- NFR6: `Result[T]` returns for fallible cache methods
+- NFR7: No new `src/<thing>.py` files
+
+## Architecture Reference
+
+- `NIL_METADATA` (child 1) — the sentinel returned by `cache.get` on miss or stale write
+- `MetadataHandle` + `MetadataHandleRegistry` (child 2) — the handle provides the cache key
+- `docs/reports/code_path_audit/2026-06-22/AUDIT_REPORT.md` Finding 1 Fix 2 — the Immediate-Mode Cache proposal
+- `src/code_path_audit_ssdl.py` — the SSDL infrastructure used to measure progress
+- `conductor/code_styleguides/data_oriented_design.md` — canonical DOD reference
+
+## Out of Scope
+
+- The 4 other `dict[str, Any]` aliases (deferred)
+- The 3 candidate placeholders (blocked)
+- Runtime profiling (Track F)
+- Eviction policy (the cache is small)
+
+## Verification Criteria (Definition of Done)
+
+| # | Criterion | Verification command |
+|---|---|---|
+| VC1 | `MetadataFieldCache` exists | `grep -rn "class MetadataFieldCache" src/` |
+| VC2 | Production code uses the cache at field-access sites | `grep -rn "field_cache.get\|field_cache.set" src/` returns ≥ 1 hit |
+| VC3 | Behavioral test exists and passes | `uv run pytest tests/test_metadata_field_cache.py -v` |
+| VC4 | Budget gate met | `compute_effective_codepaths(Metadata_profile)` returns number ≥ 30% smaller than post-child-2 measurement |
+| VC5 | Full test suite remains green | `uv run python scripts/run_tests_batched.py` → 11/11 tiers PASS |
+| VC6 | 4 audit gates remain clean | weak_types ≤ 112, type_registry in sync, main_thread_imports clean, no_models_config_io clean |
+
+## Risks
+
+| # | Risk | Likelihood | Mitigation |
+|---|---|---|---|
+| R1 | Cache invalidation is wrong (stale values returned) | medium | Cache is keyed by handle; when the underlying value changes, the handle's generation bumps (via the registry), invalidating cache entries. Behavioral test verifies the invalidation path. |
+| R2 | The 123 field-access sites are not actually 123 (audit was wrong) | low | Re-run `src.code_path_audit.detect_access_pattern_evidence` after migration to count the actual sites |
+| R3 | Budget gate fails (drop < 30%) | low | The cache collapses 123 lookups to 1 lookup each; expected to be a large drop. If not, investigate. |
\ No newline at end of file
diff --git a/conductor/tracks/metadata_field_cache_20260624/state.toml b/conductor/tracks/metadata_field_cache_20260624/state.toml
new file mode 100644
index 00000000..0dbf89a5
--- /dev/null
+++ b/conductor/tracks/metadata_field_cache_20260624/state.toml
@@ -0,0 +1,44 @@
+# Track state for metadata_field_cache_20260624
+# Child 3 of metadata_ssdl_defusing_20260624 campaign.
+# 3 phases, 3 tasks. BLOCKED_BY children 1 and 2.
+
+[meta]
+track_id = "metadata_field_cache_20260624"
+name = "Child 3: Metadata Field Cache"
+status = "active"
+current_phase = 0
+last_updated = "2026-06-24"
+
+[parent]
+parent_campaign = "metadata_ssdl_defusing_20260624"
+
+[blocked_by]
+code_path_audit_20260607 = "shipped"
+metadata_nil_sentinel_20260624 = "shipped"
+metadata_generational_handle_20260624 = "shipped"
+
+[blocks]
+# This child blocks nothing within the campaign (it's the last child)
+
+[phases]
+phase_1 = { status = "pending", checkpointsha = "", name = "Behavioral Test" }
+phase_2 = { status = "pending", checkpointsha = "", name = "Implementation (Cache + 123 migrations)" }
+phase_3 = { status = "pending", checkpointsha = "", name = "Verification + Budget Gate + Campaign SHIPPED" }
+
+[tasks]
+t1_1 = { status = "pending", commit_sha = "", description = "Write tests/test_metadata_field_cache.py with 4 tests (red)" }
+t2_1 = { status = "pending", commit_sha = "", description = "Add MetadataFieldCache + migrate 123 field-access sites" }
+t3_1 = { status = "pending", commit_sha = "", description = "Run all 6 VCs; capture budget gate; write child TRACK_COMPLETION; write campaign TRACK_COMPLETION; update both state.toml + tracks.md" }
+
+[verification]
+vc1_field_cache_exists = false
+vc2_production_uses_cache = false
+vc3_behavioral_test_passes = false
+vc4_budget_gate_met = false
+vc5_full_test_suite_green = false
+vc6_audit_gates_clean = false
+
+[budget_gate]
+baseline = "post_child_2_measurement"
+expected_drop_pct = 30
+post_child_3_measurement = null
\ No newline at end of file
diff --git a/conductor/tracks/metadata_generational_handle_20260624/metadata.json b/conductor/tracks/metadata_generational_handle_20260624/metadata.json
new file mode 100644
index 00000000..76070555
--- /dev/null
+++ b/conductor/tracks/metadata_generational_handle_20260624/metadata.json
@@ -0,0 +1,68 @@
+{
+  "track_id": "metadata_generational_handle_20260624",
+  "name": "Child 2: Metadata Generational Handle",
+  "track_type": "campaign_child",
+  "parent_campaign": "metadata_ssdl_defusing_20260624",
+  "created_date": "2026-06-24",
+  "branch": "master",
+  "depends_on": ["code_path_audit_20260607", "metadata_nil_sentinel_20260624"],
+  "blocks_within_campaign": ["metadata_field_cache_20260624"],
+  "scope": {
+    "new_files": [
+      "conductor/tracks/metadata_generational_handle_20260624/spec.md",
+      "conductor/tracks/metadata_generational_handle_20260624/plan.md",
+      "conductor/tracks/metadata_generational_handle_20260624/metadata.json",
+      "conductor/tracks/metadata_generational_handle_20260624/state.toml",
+      "tests/test_metadata_generational_handle.py",
+      "docs/reports/TRACK_COMPLETION_metadata_generational_handle_20260624.md"
+    ],
+    "modified_files": [
+      "src/aggregate.py (MetadataHandle + Registry types + lifetime-check migrations)",
+      "src/ai_client.py (lifetime-check migrations; specific files TBD by Tier 2)",
+      "conductor/tracks.md",
+      "docs/reports/campaign_measurements_20260624.md"
+    ],
+    "deleted_files": []
+  },
+  "estimated_effort": {
+    "method": "scope (per workflow.md §Tier 1 Track Initialization Rules). NO day estimates.",
+    "phase_1": "1 task: 4 behavioral tests",
+    "phase_2": "1 task: MetadataHandle + Registry + lifetime-check migrations",
+    "phase_3": "1 task: 6 VCs + budget gate + TRACK_COMPLETION + state + tracks.md"
+  },
+  "verification_criteria": [
+    "VC1: MetadataHandle + MetadataHandleRegistry exist",
+    "VC2: Production code uses handle + registry at entry points",
+    "VC3: Behavioral test exists and passes",
+    "VC4: Budget gate met (drop >= 20% vs post-child-1 measurement)",
+    "VC5: Full test suite remains green (11/11 tiers PASS)",
+    "VC6: 4 audit gates remain clean"
+  ],
+  "known_issues": [],
+  "deferred_to_followup_tracks": [],
+  "regressions_and_pre_existing_failures": [],
+  "pre_existing_failures_remaining": [],
+  "risk_register": [
+    {
+      "id": "risk-1",
+      "description": "The handle breaks code that expects raw Metadata",
+      "likelihood": "medium",
+      "impact": "Production code that does entry['key'] directly fails",
+      "mitigation": "Handle is a wrapper; consumers can extract raw value via .value; behavioral test verifies backwards-compat"
+    },
+    {
+      "id": "risk-2",
+      "description": "The registry's lookup is not actually O(1)",
+      "likelihood": "low",
+      "impact": "Cache pattern in child 3 doesn't work as expected",
+      "mitigation": "Registry uses dict[int, int]; lookup is O(1) by construction"
+    },
+    {
+      "id": "risk-3",
+      "description": "Budget gate fails (drop < 20%)",
+      "likelihood": "low",
+      "impact": "Child 2 cannot ship; campaign pauses",
+      "mitigation": "3466 branch points include lifetime checks; replacing with handle lookup should drop the count"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/conductor/tracks/metadata_generational_handle_20260624/plan.md b/conductor/tracks/metadata_generational_handle_20260624/plan.md
new file mode 100644
index 00000000..3e017fb3
--- /dev/null
+++ b/conductor/tracks/metadata_generational_handle_20260624/plan.md
@@ -0,0 +1,79 @@
+# Plan: metadata_generational_handle_20260624
+
+3 tasks, 3 atomic commits. Same pattern as child 1.
+
+## Phase 1: Behavioral Test (1 task)
+
+- [ ] Task 1.1: Write `tests/test_metadata_generational_handle.py`.
+  - WHERE: New file `tests/test_metadata_generational_handle.py`
+  - WHAT: 4 tests (per spec FR3)
+  - HOW: Use 1-space indentation
+  - SAFETY: Test imports `MetadataHandle` and `MetadataHandleRegistry` from their production location
+  - COMMIT: `test(metadata): behavioral test for generational handle (MetadataHandle + Registry)`
+  - GIT NOTE: 4 tests; will be RED until Phase 2 ships
+  - VERIFY: `uv run pytest tests/test_metadata_generational_handle.py -v` shows 4/4 FAIL (expected)
+
+## Phase 2: Implementation (1 task)
+
+- [ ] Task 2.1: Add `MetadataHandle` + `MetadataHandleRegistry` + migrate lifetime-check code.
+  - WHERE: `src/aggregate.py` (or another existing module; no new `src/<thing>.py` files)
+  - WHAT:
+    - Add `@dataclass(frozen=True) class MetadataHandle` with `index: int` and `generation: int`
+    - Add `class MetadataHandleRegistry` with `register`, `lookup`, `bump_generation` methods
+    - Migrate lifetime-check sites in `src/aggregate.py`, `src/ai_client.py`, and any other production files
+  - HOW: Use `manual-slop_py_add_def` for the new types; `manual-slop_edit_file` for the migration sites
+  - SAFETY: Verify with `ast.parse`; run the 4 tests + the child-1 tests + the 14 previously-failing tests
+  - COMMIT: `feat(metadata): MetadataHandle + Registry + lifetime-check migrations`
+  - GIT NOTE: Lifetime checks now go through registry.lookup; generation mismatch returns NIL_METADATA from child 1
+  - VERIFY: `uv run pytest tests/test_metadata_generational_handle.py tests/test_metadata_nil_sentinel.py -v` shows all PASS
+
+## Phase 3: Verification + Budget Gate (1 task)
+
+- [ ] Task 3.1: Run all 6 VCs; capture the budget gate measurement.
+  - WHERE: All audit gates + test suite + SSDL measurement
+  - WHAT:
+    - Run VC1-VC6
+    - Compute the new effective-codepaths number
+    - Compare to post-child-1 measurement; require drop ≥ 20%
+    - Write TRACK_COMPLETION report
+    - Update state.toml to `status = "completed"`, all 3 phases completed
+    - Append to campaign_measurements_20260624.md
+    - Update conductor/tracks.md
+  - HOW: Same as child 1 phase 3
+  - SAFETY: Same as child 1
+  - COMMIT: 3 commits (state, TRACK_COMPLETION, tracks.md)
+  - GIT NOTE: Per workflow.md
+  - VERIFY: All 6 VCs pass; budget gate met; campaign unblocked for child 3
+
+## Commit Log (Expected)
+
+1. `test(metadata): behavioral test for generational handle` (Task 1.1)
+2. `feat(metadata): MetadataHandle + Registry + lifetime-check migrations` (Task 2.1)
+3. `conductor(state): metadata_generational_handle_20260624 SHIPPED` (Task 3.1)
+4. `docs(reports): TRACK_COMPLETION for metadata_generational_handle_20260624` (Task 3.1)
+5. `conductor(tracks): add metadata_generational_handle_20260624 row` (Task 3.1)
+
+## Verification Commands
+
+```bash
+# VC1: types exist
+grep -rn "class MetadataHandle\|class MetadataHandleRegistry" src/
+
+# VC2: production uses handle
+grep -rn "registry.lookup\|registry.register" src/
+
+# VC3: tests pass
+uv run pytest tests/test_metadata_generational_handle.py -v
+
+# VC4: budget gate
+uv run python -c "from src.code_path_audit_ssdl import compute_effective_codepaths; ...; print(compute_effective_codepaths(metadata_profile, 'src'))"
+
+# VC5: full test suite
+uv run python scripts/run_tests_batched.py
+
+# VC6: 4 audit gates
+uv run python scripts/audit_weak_types.py --strict
+uv run python scripts/generate_type_registry.py --check
+uv run python scripts/audit_main_thread_imports.py
+uv run python scripts/audit_no_models_config_io.py
+```
\ No newline at end of file
diff --git a/conductor/tracks/metadata_generational_handle_20260624/spec.md b/conductor/tracks/metadata_generational_handle_20260624/spec.md
new file mode 100644
index 00000000..066bd9b4
--- /dev/null
+++ b/conductor/tracks/metadata_generational_handle_20260624/spec.md
@@ -0,0 +1,115 @@
+# Track Specification: metadata_generational_handle_20260624
+
+## Overview
+
+Child 2 of the `metadata_ssdl_defusing_20260624` campaign. Wraps `Metadata` in a `(index, generation)` handle resolved through a registry. Collapses lifetime branches to 1 lookup + 1 generation comparison. **BLOCKED_BY child 1** (the nil sentinel is the fallback path on generation mismatch).
+
+## Current State Audit (master @ child-1-SHIPPED, after metadata_nil_sentinel_20260624)
+
+- `NIL_METADATA` sentinel exists (from child 1)
+- The 6 nil-check functions use sentinel-return
+- The 3466 branch points in the parent audit include lifetime checks (e.g., "is this handle still valid?")
+- `src/aggregate.py` and `src/ai_client.py` contain lifetime checks; they should be replaced with handle lookup + generation comparison
+
+## Goals
+
+| ID | Goal | Acceptance |
+|---|---|---|
+| G1 | `MetadataHandle` (or equivalent) introduced: a `(index: int, generation: int)` pair | The handle type is exported; can be created and queried |
+| G2 | `MetadataHandleRegistry` (or equivalent) introduced: stores `index -> generation` mapping | The registry has O(1) lookup, bump-generation, and get-with-validation methods |
+| G3 | Production `Metadata` is wrapped in a handle at the consumer entry points | Consumers can do `handle.registry_lookup()` instead of `if entry.lifetime != current_lifetime: ...` |
+| G4 | 1 behavioral test for the handle | `tests/test_metadata_generational_handle.py` exists; asserts lookup, generation mismatch returns `NIL_METADATA`, bump invalidates cached lookups |
+| G5 | Budget gate met: effective-codepaths drop ≥ 20% vs post-child-1 measurement | Re-measurement shows the drop |
+
+## Non-Goals
+
+- Touching the 4 other `dict[str, Any]` aliases — out of scope (deferred to follow-up campaign)
+- Touching the list-typed aggregates — out of scope
+- Replacing the 3 candidate placeholders — blocked on `any_type_componentization_20260621`
+- Adding a generational handle for the inner Metadata values within nested structures (the campaign handles the top-level Metadata; nested handles are out of scope)
+- Cache invalidation (that's child 3; this child just provides the identity)
+
+## Functional Requirements
+
+### FR1: Handle + Registry types
+
+In a sensible location (likely `src/aggregate.py` per AGENTS.md §File Naming Convention, OR a NEW module if the user explicitly approves):
+
+```python
+@dataclass(frozen=True)
+class MetadataHandle:
+    index: int
+    generation: int
+
+class MetadataHandleRegistry:
+    def __init__(self) -> None:
+        self._generations: dict[int, int] = {}
+    
+    def register(self, metadata: Metadata) -> MetadataHandle:
+        # returns a new handle with a fresh index + generation
+    
+    def lookup(self, handle: MetadataHandle) -> Metadata | None:
+        # if handle.generation != self._generations[handle.index], return None
+        # otherwise return the stored Metadata (or sentinel for now)
+    
+    def bump_generation(self, index: int) -> None:
+        # invalidate the cached entry for this index
+```
+
+(Exact API up to Tier 2; the contract is: handle + registry with O(1) lookup + generation-based invalidation.)
+
+### FR2: Migrate lifetime-branch code
+
+For each site in `src/` that does lifetime checks (e.g., "is this Metadata still the one I cached?"):
+- Replace with `handle = registry.register(metadata)` + `value = registry.lookup(handle)` + `if value is None: use NIL_METADATA`
+
+### FR3: Behavioral test
+
+`tests/test_metadata_generational_handle.py` with at least 3 tests:
+- `test_register_returns_handle`: assert `registry.register(metadata)` returns a `MetadataHandle` with distinct `index` and `generation`
+- `test_lookup_returns_none_after_bump`: assert `registry.lookup(handle)` returns None after `registry.bump_generation(handle.index)`
+- `test_lookup_returns_none_for_unknown_index`: assert `registry.lookup(MetadataHandle(index=999, generation=1))` returns None
+- `test_lookup_returns_value_for_valid_handle`: assert `registry.lookup(handle)` returns the registered Metadata
+
+## Non-Functional Requirements
+
+- NFR1: 1-space indentation
+- NFR2: CRLF line endings on Windows
+- NFR3: No comments in source code
+- NFR4: Per-task atomic commits with git notes
+- NFR5: No new pip dependencies
+- NFR6: `Result[T]` returns for fallible registry methods (per `conductor/code_styleguides/error_handling.md`)
+- NFR7: No new `src/<thing>.py` files (per AGENTS.md) — unless the user explicitly approves; default is to put `MetadataHandle` + `MetadataHandleRegistry` in `src/aggregate.py` or another existing module
+
+## Architecture Reference
+
+- `src/aggregate.py` (the parent module for `Metadata`)
+- `NIL_METADATA` (from child 1) — the fallback returned by `lookup` on generation mismatch
+- `docs/reports/code_path_audit/2026-06-22/AUDIT_REPORT.md` Finding 1 Fix 3 — the Generational Handle proposal
+- `conductor/code_styleguides/data_oriented_design.md` — canonical DOD reference
+
+## Out of Scope
+
+- The 4 other `dict[str, Any]` aliases (deferred)
+- The 3 candidate placeholders (blocked)
+- The cache (child 3)
+- Runtime profiling (Track F from the previous menu; deferred)
+
+## Verification Criteria (Definition of Done)
+
+| # | Criterion | Verification command |
+|---|---|---|
+| VC1 | `MetadataHandle` and `MetadataHandleRegistry` exist | `grep -rn "class MetadataHandle\|class MetadataHandleRegistry" src/` |
+| VC2 | Production code uses handle + registry at the entry points | `grep -rn "registry.lookup\|registry.register" src/` returns ≥ 1 hit |
+| VC3 | Behavioral test exists and passes | `uv run pytest tests/test_metadata_generational_handle.py -v` |
+| VC4 | Budget gate met | `compute_effective_codepaths(Metadata_profile)` returns number ≥ 20% smaller than post-child-1 measurement |
+| VC5 | Full test suite remains green | `uv run python scripts/run_tests_batched.py` → 11/11 tiers PASS |
+| VC6 | 4 audit gates remain clean | weak_types ≤ 112, type_registry in sync, main_thread_imports clean, no_models_config_io clean |
+
+## Risks
+
+| # | Risk | Likelihood | Mitigation |
+|---|---|---|---|
+| R1 | The handle breaks code that expects raw `Metadata` | medium | The handle is a wrapper; consumers can extract the raw value via `.value` or similar. Behavioral test verifies backwards-compat for the common cases. |
+| R2 | The registry's lookup is not actually O(1) | low | The registry uses a `dict[int, int]` for `index -> generation`; lookup is O(1) by construction. |
+| R3 | Budget gate fails (drop < 20%) | low | The 3466 branch points include lifetime checks; replacing with handle lookup should drop the count. If not, the SSDL math is wrong. |
\ No newline at end of file
diff --git a/conductor/tracks/metadata_generational_handle_20260624/state.toml b/conductor/tracks/metadata_generational_handle_20260624/state.toml
new file mode 100644
index 00000000..b9569e7c
--- /dev/null
+++ b/conductor/tracks/metadata_generational_handle_20260624/state.toml
@@ -0,0 +1,44 @@
+# Track state for metadata_generational_handle_20260624
+# Child 2 of metadata_ssdl_defusing_20260624 campaign.
+# 3 phases, 3 tasks. BLOCKED_BY child 1.
+
+[meta]
+track_id = "metadata_generational_handle_20260624"
+name = "Child 2: Metadata Generational Handle"
+status = "active"
+current_phase = 0
+last_updated = "2026-06-24"
+
+[parent]
+parent_campaign = "metadata_ssdl_defusing_20260624"
+
+[blocked_by]
+code_path_audit_20260607 = "shipped"
+metadata_nil_sentinel_20260624 = "shipped"
+
+[blocks]
+# Within the campaign:
+metadata_field_cache_20260624 = "pending child 2"
+
+[phases]
+phase_1 = { status = "pending", checkpointsha = "", name = "Behavioral Test" }
+phase_2 = { status = "pending", checkpointsha = "", name = "Implementation (Handle + Registry + migrations)" }
+phase_3 = { status = "pending", checkpointsha = "", name = "Verification + Budget Gate" }
+
+[tasks]
+t1_1 = { status = "pending", commit_sha = "", description = "Write tests/test_metadata_generational_handle.py with 4 tests (red)" }
+t2_1 = { status = "pending", commit_sha = "", description = "Add MetadataHandle + MetadataHandleRegistry + migrate lifetime-check sites" }
+t3_1 = { status = "pending", commit_sha = "", description = "Run all 6 VCs; capture budget gate measurement; write TRACK_COMPLETION; update state + tracks.md" }
+
+[verification]
+vc1_handle_and_registry_exist = false
+vc2_production_uses_registry = false
+vc3_behavioral_test_passes = false
+vc4_budget_gate_met = false
+vc5_full_test_suite_green = false
+vc6_audit_gates_clean = false
+
+[budget_gate]
+baseline = "post_child_1_measurement"
+expected_drop_pct = 20
+post_child_2_measurement = null
\ No newline at end of file
diff --git a/conductor/tracks/metadata_nil_sentinel_20260624/metadata.json b/conductor/tracks/metadata_nil_sentinel_20260624/metadata.json
new file mode 100644
index 00000000..f646df74
--- /dev/null
+++ b/conductor/tracks/metadata_nil_sentinel_20260624/metadata.json
@@ -0,0 +1,68 @@
+{
+  "track_id": "metadata_nil_sentinel_20260624",
+  "name": "Child 1: Metadata Nil Sentinel",
+  "track_type": "campaign_child",
+  "parent_campaign": "metadata_ssdl_defusing_20260624",
+  "created_date": "2026-06-24",
+  "branch": "master",
+  "depends_on": ["code_path_audit_20260607"],
+  "blocks_within_campaign": ["metadata_generational_handle_20260624"],
+  "scope": {
+    "new_files": [
+      "conductor/tracks/metadata_nil_sentinel_20260624/spec.md",
+      "conductor/tracks/metadata_nil_sentinel_20260624/plan.md",
+      "conductor/tracks/metadata_nil_sentinel_20260624/metadata.json",
+      "conductor/tracks/metadata_nil_sentinel_20260624/state.toml",
+      "tests/test_metadata_nil_sentinel.py",
+      "docs/reports/TRACK_COMPLETION_metadata_nil_sentinel_20260624.md"
+    ],
+    "modified_files": [
+      "src/aggregate.py (NIL_METADATA constant + nil-check migrations)",
+      "src/ai_client.py (nil-check migrations; specific files TBD by Tier 2)",
+      "conductor/tracks.md",
+      "docs/reports/campaign_measurements_20260624.md"
+    ],
+    "deleted_files": []
+  },
+  "estimated_effort": {
+    "method": "scope (per workflow.md §Tier 1 Track Initialization Rules). NO day estimates.",
+    "phase_1": "1 task: write the 2 behavioral tests",
+    "phase_2": "1 task: NIL_METADATA constant + 6 nil-check migrations",
+    "phase_3": "1 task: 6 VCs + budget gate + TRACK_COMPLETION + state + tracks.md"
+  },
+  "verification_criteria": [
+    "VC1: NIL_METADATA is defined in src/",
+    "VC2: The 6 nil-check functions no longer have the 3-pattern nil-check",
+    "VC3: Behavioral test exists and passes",
+    "VC4: Budget gate met (drop >= 10% vs 4.01e22 baseline)",
+    "VC5: Full test suite remains green (11/11 tiers PASS)",
+    "VC6: 4 audit gates remain clean"
+  ],
+  "known_issues": [],
+  "deferred_to_followup_tracks": [],
+  "regressions_and_pre_existing_failures": [],
+  "pre_existing_failures_remaining": [],
+  "risk_register": [
+    {
+      "id": "risk-1",
+      "description": "The 6 nil-check functions are in unexpected locations",
+      "likelihood": "low",
+      "impact": "Phase 2 needs to find them via grep + detect_nil_check_pattern",
+      "mitigation": "Audit enumerated all consumer files; detect_nil_check_pattern is the oracle"
+    },
+    {
+      "id": "risk-2",
+      "description": "NIL_METADATA defaults cause downstream bugs",
+      "likelihood": "low",
+      "impact": "Production code that uses the sentinel crashes",
+      "mitigation": "Empty defaults + behavioral test verifies sentinel works in a real call"
+    },
+    {
+      "id": "risk-3",
+      "description": "Budget gate fails (drop < 10%)",
+      "likelihood": "low",
+      "impact": "Child 1 cannot ship; campaign pauses",
+      "mitigation": "The 6 nil-checks are documented; their removal MUST drop the branch count"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/conductor/tracks/metadata_nil_sentinel_20260624/plan.md b/conductor/tracks/metadata_nil_sentinel_20260624/plan.md
new file mode 100644
index 00000000..f77e0871
--- /dev/null
+++ b/conductor/tracks/metadata_nil_sentinel_20260624/plan.md
@@ -0,0 +1,92 @@
+# Plan: metadata_nil_sentinel_20260624
+
+3 tasks, 3 atomic commits. TDD: write the test first (red), implement (green), commit.
+
+## Phase 1: Behavioral Test (1 task)
+
+Focus: Write the failing test for the sentinel.
+
+- [ ] Task 1.1: Write `tests/test_metadata_nil_sentinel.py`.
+  - WHERE: New file `tests/test_metadata_nil_sentinel.py`
+  - WHAT: 2 tests:
+    - `test_nil_metadata_is_defined`: `from src.aggregate import NIL_METADATA; assert NIL_METADATA is not None; assert isinstance(NIL_METADATA, dict) or isinstance(NIL_METADATA, Metadata)` (depending on whether Metadata is a TypeAlias or class)
+    - `test_detect_nil_check_pattern_returns_false_for_migrated_functions`: import the 6 migrated functions; assert `detect_nil_check_pattern` returns False for each
+  - HOW: Use the existing `src/code_path_audit_ssdl.detect_nil_check_pattern` as the oracle. Use 1-space indentation.
+  - SAFETY: The test file imports the 6 functions. Identify them by running `grep` for `is None` patterns in `src/aggregate.py` and `src/ai_client.py`. If Tier 2 finds additional functions in other files, include them too.
+  - COMMIT: `test(metadata): behavioral test for nil sentinel (NIL_METADATA)`
+  - GIT NOTE: 2 tests, imports the 6 functions, asserts detect_nil_check_pattern returns False for each; will be RED until Phase 2 ships
+  - VERIFY: `uv run pytest tests/test_metadata_nil_sentinel.py -v` shows 2/2 FAIL (expected; the sentinel doesn't exist yet)
+
+## Phase 2: Implementation (1 task)
+
+Focus: Define `NIL_METADATA` and migrate the 6 functions.
+
+- [ ] Task 2.1: Add `NIL_METADATA` and migrate the 6 nil-check functions.
+  - WHERE: `src/aggregate.py` (NIL_METADATA constant) + the 6 files containing the nil-check functions (likely `src/aggregate.py` and `src/ai_client.py`)
+  - WHAT:
+    - Add `NIL_METADATA: Metadata = Metadata(...)` constant in `src/aggregate.py` (the defaults are safe; an empty `{}` if Metadata is a TypeAlias)
+    - For each of the 6 nil-check functions, replace the `if entry is None: ...` / `if entry == None: ...` / `if entry != None: ...` pattern with sentinel-return
+    - The most common pattern: `entry = entry or NIL_METADATA` at the top of the function (replaces the `if entry is None: return default` early-return)
+  - HOW: Use `manual-slop_edit_file` for each migration site. Use `manual-slop_py_add_def` for the `NIL_METADATA` constant.
+  - SAFETY:
+    - Verify with `ast.parse(open("src/aggregate.py").read())`
+    - Run `uv run pytest tests/test_metadata_nil_sentinel.py -v` → 2/2 PASS
+    - Run the 14 previously-failing tests from `fix_test_failures_20260624` → 14/14 PASS (no regression)
+  - COMMIT: `feat(metadata): NIL_METADATA sentinel + 6 nil-check migrations`
+  - GIT NOTE: 6 functions refactored to use sentinel-return; established the fallback that child 2's generation-mismatch path returns to
+  - VERIFY: `uv run pytest tests/test_metadata_nil_sentinel.py -v` shows 2/2 PASS
+
+## Phase 3: Verification + Budget Gate (1 task)
+
+Focus: Run all 6 VCs + the budget gate.
+
+- [ ] Task 3.1: Run all 6 VCs; capture the budget gate measurement.
+  - WHERE: All audit gates + test suite + SSDL measurement
+  - WHAT:
+    - Run VC1-VC6 (the 6 verification criteria from the spec)
+    - Compute the new effective-codepaths number: `uv run python -c "from src.code_path_audit_ssdl import compute_effective_codepaths; from src.code_path_audit import AggregateProfile, ...; profile = ...; print(compute_effective_codepaths(profile, 'src'))"`
+    - Compute the drop vs 4.01e22 baseline; if drop ≥ 10%, mark the budget gate as PASS
+    - Write the child's TRACK_COMPLETION report at `docs/reports/TRACK_COMPLETION_metadata_nil_sentinel_20260624.md`
+    - Update this track's `state.toml` to `status = "completed"`, `current_phase = "complete"`, all 3 phases `completed`
+    - Append the post-child-1 measurement to `docs/reports/campaign_measurements_20260624.md` (the campaign-level log)
+    - Update `conductor/tracks.md` to add a row for this child
+  - HOW: Run each VC command, capture output, write the report.
+  - SAFETY: The 2 pre-existing-violation audit gates (NG1, NG2 from `code_path_audit_polish_20260622`) are still out of scope. Do not regress them.
+  - COMMIT: 3 commits: `conductor(state): metadata_nil_sentinel_20260624 SHIPPED`, `docs(reports): TRACK_COMPLETION for metadata_nil_sentinel_20260624`, `conductor(tracks): add metadata_nil_sentinel_20260624 row`
+  - GIT NOTE: 1 per commit per workflow.md
+  - VERIFY: All 6 VCs pass; budget gate met (drop ≥ 10%); campaign unblocked for child 2
+
+## Commit Log (Expected)
+
+1. `test(metadata): behavioral test for nil sentinel (NIL_METADATA)` (Task 1.1)
+2. `feat(metadata): NIL_METADATA sentinel + 6 nil-check migrations` (Task 2.1)
+3. `conductor(state): metadata_nil_sentinel_20260624 SHIPPED` (Task 3.1)
+4. `docs(reports): TRACK_COMPLETION for metadata_nil_sentinel_20260624` (Task 3.1)
+5. `conductor(tracks): add metadata_nil_sentinel_20260624 row` (Task 3.1)
+
+Plus per-task plan-update commits per the workflow.
+
+## Verification Commands (run at end of Phase 3)
+
+```bash
+# VC1: NIL_METADATA defined
+grep -rn "NIL_METADATA" src/
+
+# VC2: detect_nil_check_pattern returns False for the 6 functions
+uv run python -c "from src.code_path_audit_ssdl import detect_nil_check_pattern; from src.code_path_audit import FunctionRef; ...; [assert not detect_nil_check_pattern(f, 'src') for f in the_6_functions]"
+
+# VC3: behavioral test
+uv run pytest tests/test_metadata_nil_sentinel.py -v
+
+# VC4: budget gate (measure and compare)
+uv run python -c "from src.code_path_audit_ssdl import compute_effective_codepaths; ...; print(compute_effective_codepaths(metadata_profile, 'src'))"
+
+# VC5: full test suite
+uv run python scripts/run_tests_batched.py
+
+# VC6: 4 audit gates
+uv run python scripts/audit_weak_types.py --strict
+uv run python scripts/generate_type_registry.py --check
+uv run python scripts/audit_main_thread_imports.py
+uv run python scripts/audit_no_models_config_io.py
+```
\ No newline at end of file
diff --git a/conductor/tracks/metadata_nil_sentinel_20260624/spec.md b/conductor/tracks/metadata_nil_sentinel_20260624/spec.md
new file mode 100644
index 00000000..7c599bdd
--- /dev/null
+++ b/conductor/tracks/metadata_nil_sentinel_20260624/spec.md
@@ -0,0 +1,98 @@
+# Track Specification: metadata_nil_sentinel_20260624
+
+## Overview
+
+Child 1 of the `metadata_ssdl_defusing_20260624` campaign. Introduces `NIL_METADATA = Metadata(...)` sentinel and migrates the 6 nil-check functions identified by the parent audit. Establishes the fallback path that Child 2 (Generational Handle) returns to on generation mismatch.
+
+## Current State Audit (master @ 7a9261c4)
+
+- `src/aggregate.py` and `src/ai_client.py` contain 6 functions with `is None` / `== None` / `!= None` patterns on `Metadata` (or aliases of `dict[str, Any]`). These are detected by `src/code_path_audit_ssdl.detect_nil_check_pattern`.
+- The parent audit (`docs/reports/code_path_audit/2026-06-22/AUDIT_REPORT.md` Finding 1) reports "6 nil-check functions" and "4.01e22 effective codepaths" for the `Metadata` aggregate.
+- No `NIL_METADATA` constant exists.
+
+## Goals
+
+| ID | Goal | Acceptance |
+|---|---|---|
+| G1 | `NIL_METADATA = Metadata(...)` constant exists in the production source | `grep -rn "NIL_METADATA" src/` finds the constant + the 6 migration sites |
+| G2 | The 6 nil-check functions use the sentinel | `src.code_path_audit_ssdl.detect_nil_check_pattern` returns 0 for the 6 functions after migration |
+| G3 | 1 behavioral test for the sentinel | `tests/test_metadata_nil_sentinel.py` exists; all assertions pass |
+| G4 | Budget gate met: effective-codepaths drop ≥ 10% vs 4.01e22 baseline | `compute_effective_codepaths(Metadata_profile)` returns a number ≥ 10% smaller than 4.01e22 |
+
+## Non-Goals
+
+- Touching the 4 other `dict[str, Any]` aliases (FileItem, CommsLogEntry, HistoryMessage, ToolDefinition, ToolCall) — they have similar patterns (parent audit Finding 2) but are out of scope for this child
+- Touching the list-typed aggregates (CommsLog, History, FileItems) — out of scope
+- Touching the 3 candidate aggregates (ToolSpec, ChatMessage, ProviderHistory) — blocked on `any_type_componentization_20260621` (NOT on master)
+- Refactoring the 6 functions beyond the nil-check migration (the change is surgical: replace the nil-check with sentinel-return)
+- Adding new audit infrastructure (the campaign USES the existing SSDL functions)
+
+## Functional Requirements
+
+### FR1: Define `NIL_METADATA`
+
+In a sensible location (likely `src/aggregate.py` since it's the Metadata parent module per `src/code_path_audit.py:343-368`'s `CANONICAL_MEMORY_DIM`), add:
+
+```python
+NIL_METADATA: Metadata = Metadata(
+    # safe defaults; the exact contents are up to Tier 2
+)
+```
+
+The defaults MUST be safe (no-op / no-value) such that consumers can blindly use `entry or NIL_METADATA` without triggering KeyError or AttributeError.
+
+### FR2: Migrate the 6 nil-check functions
+
+For each of the 6 functions detected by `src/code_path_audit_ssdl.detect_nil_check_pattern`:
+- Replace `if entry is None: ...` / `if entry is None or entry == "": ...` / `if entry != None: ...` patterns with sentinel-return
+- The most common pattern: `entry = entry or NIL_METADATA` at the top of the function
+- Preserve the function's existing behavior for non-nil cases
+
+### FR3: Behavioral test
+
+`tests/test_metadata_nil_sentinel.py` with at least 2 tests:
+- `test_nil_metadata_is_defined`: assert `NIL_METADATA` exists and is a valid `Metadata` (or `dict[str, Any]` if Metadata is a TypeAlias)
+- `test_migrated_function_uses_sentinel`: call one of the 6 migrated functions with `None` and assert it returns the sentinel (or behavior equivalent to using the sentinel)
+
+## Non-Functional Requirements
+
+- NFR1: 1-space indentation
+- NFR2: CRLF line endings on Windows
+- NFR3: No comments in source code
+- NFR4: Per-task atomic commits with git notes
+- NFR5: No new pip dependencies
+- NFR6: The 6 migration sites use the existing convention (sentinel pattern, not new abstractions)
+- NFR7: No new `src/<thing>.py` files (per AGENTS.md) — `NIL_METADATA` lives in `src/aggregate.py` or another existing module
+
+## Architecture Reference
+
+- `src/code_path_audit_ssdl.py:84-100` — `detect_nil_check_pattern` (the function that identifies the 6 sites)
+- `src/code_path_audit.py:343-368` — `CANONICAL_MEMORY_DIM` (where Metadata's canonical location is)
+- `src/aggregate.py` — the parent module for `Metadata`
+- `docs/reports/code_path_audit/2026-06-22/AUDIT_REPORT.md` Finding 1 — the 6 nil-check functions and the proposed fix
+- `conductor/code_styleguides/data_oriented_design.md` — the canonical DOD reference
+
+## Out of Scope
+
+- All other aggregates (deferred to a follow-up campaign)
+- The 3 candidate aggregates (blocked on `any_type_componentization_20260621`)
+- Runtime profiling (Track F from the previous menu; deferred)
+
+## Verification Criteria (Definition of Done)
+
+| # | Criterion | Verification command |
+|---|---|---|
+| VC1 | `NIL_METADATA` is defined in `src/` | `grep -rn "NIL_METADATA" src/` returns ≥ 1 hit |
+| VC2 | The 6 nil-check functions no longer have the 3-pattern nil-check | `src/code_path_audit_ssdl.detect_nil_check_pattern` returns False for all 6 |
+| VC3 | Behavioral test exists and passes | `uv run pytest tests/test_metadata_nil_sentinel.py -v` |
+| VC4 | Budget gate met | `compute_effective_codepaths(Metadata_profile)` returns number ≥ 10% smaller than 4.01e22 |
+| VC5 | Full test suite remains green | `uv run python scripts/run_tests_batched.py` → 11/11 tiers PASS |
+| VC6 | 4 audit gates remain clean | weak_types ≤ 112, type_registry in sync, main_thread_imports clean, no_models_config_io clean |
+
+## Risks
+
+| # | Risk | Likelihood | Mitigation |
+|---|---|---|---|
+| R1 | The 6 nil-check functions are in unexpected locations (not aggregate.py or ai_client.py) | low | `detect_nil_check_pattern` enumerates all consumer files; the audit identified them |
+| R2 | The `NIL_METADATA` defaults are wrong (cause downstream bugs) | low | The defaults should be safe (empty Metadata with no required fields). Behavioral test verifies sentinel works in a real call. |
+| R3 | Budget gate fails (drop < 10%) | low | The 6 nil-checks are documented; their removal MUST drop. If not, the SSDL math is wrong (separate investigation). |
\ No newline at end of file
diff --git a/conductor/tracks/metadata_nil_sentinel_20260624/state.toml b/conductor/tracks/metadata_nil_sentinel_20260624/state.toml
new file mode 100644
index 00000000..6a697876
--- /dev/null
+++ b/conductor/tracks/metadata_nil_sentinel_20260624/state.toml
@@ -0,0 +1,43 @@
+# Track state for metadata_nil_sentinel_20260624
+# Child 1 of metadata_ssdl_defusing_20260624 campaign.
+# 3 phases, 3 tasks. Tier 2 to execute per conductor/workflow.md.
+
+[meta]
+track_id = "metadata_nil_sentinel_20260624"
+name = "Child 1: Metadata Nil Sentinel"
+status = "active"
+current_phase = 0
+last_updated = "2026-06-24"
+
+[parent]
+parent_campaign = "metadata_ssdl_defusing_20260624"
+
+[blocked_by]
+code_path_audit_20260607 = "shipped"
+
+[blocks]
+# Within the campaign:
+metadata_generational_handle_20260624 = "pending child 1"
+
+[phases]
+phase_1 = { status = "pending", checkpointsha = "", name = "Behavioral Test" }
+phase_2 = { status = "pending", checkpointsha = "", name = "Implementation (NIL_METADATA + 6 migrations)" }
+phase_3 = { status = "pending", checkpointsha = "", name = "Verification + Budget Gate" }
+
+[tasks]
+t1_1 = { status = "pending", commit_sha = "", description = "Write tests/test_metadata_nil_sentinel.py with 2 tests (red)" }
+t2_1 = { status = "pending", commit_sha = "", description = "Add NIL_METADATA constant + migrate 6 nil-check functions" }
+t3_1 = { status = "pending", commit_sha = "", description = "Run all 6 VCs; capture budget gate measurement; write TRACK_COMPLETION; update state + tracks.md" }
+
+[verification]
+vc1_nil_metadata_defined = false
+vc2_6_nil_checks_migrated = false
+vc3_behavioral_test_passes = false
+vc4_budget_gate_met = false
+vc5_full_test_suite_green = false
+vc6_audit_gates_clean = false
+
+[budget_gate]
+baseline = 4.01e+22
+expected_drop_pct = 10
+post_child_1_measurement = null
\ No newline at end of file
diff --git a/conductor/tracks/metadata_ssdl_defusing_20260624/metadata.json b/conductor/tracks/metadata_ssdl_defusing_20260624/metadata.json
new file mode 100644
index 00000000..2294b730
--- /dev/null
+++ b/conductor/tracks/metadata_ssdl_defusing_20260624/metadata.json
@@ -0,0 +1,132 @@
+{
+  "track_id": "metadata_ssdl_defusing_20260624",
+  "name": "Metadata SSDL Defusing Campaign",
+  "track_type": "campaign",
+  "created_date": "2026-06-24",
+  "branch": "master",
+  "depends_on": ["code_path_audit_20260607"],
+  "blocks": [],
+  "child_tracks": [
+    {
+      "track_id": "metadata_nil_sentinel_20260624",
+      "name": "Child 1: Nil Sentinel",
+      "blocked_by_parent": false,
+      "blocks_within_campaign": ["metadata_generational_handle_20260624"]
+    },
+    {
+      "track_id": "metadata_generational_handle_20260624",
+      "name": "Child 2: Generational Handle",
+      "blocked_by_parent": true,
+      "blocks_within_campaign": ["metadata_field_cache_20260624"]
+    },
+    {
+      "track_id": "metadata_field_cache_20260624",
+      "name": "Child 3: Immediate-Mode Field Cache",
+      "blocked_by_parent": true,
+      "blocks_within_campaign": []
+    }
+  ],
+  "scope": {
+    "new_files": [
+      "conductor/tracks/metadata_ssdl_defusing_20260624/spec.md",
+      "conductor/tracks/metadata_ssdl_defusing_20260624/plan.md",
+      "conductor/tracks/metadata_ssdl_defusing_20260624/metadata.json",
+      "conductor/tracks/metadata_ssdl_defusing_20260624/state.toml",
+      "conductor/tracks/metadata_nil_sentinel_20260624/*",
+      "conductor/tracks/metadata_generational_handle_20260624/*",
+      "conductor/tracks/metadata_field_cache_20260624/*",
+      "tests/test_metadata_nil_sentinel.py",
+      "tests/test_metadata_generational_handle.py",
+      "tests/test_metadata_field_cache.py",
+      "docs/reports/campaign_measurements_20260624.md",
+      "docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md"
+    ],
+    "modified_files": [
+      "src/aggregate.py",
+      "src/ai_client.py",
+      "src/history.py",
+      "src/aggregate.py (additional functions as Tier 2 identifies)",
+      "conductor/tracks.md"
+    ],
+    "deleted_files": []
+  },
+  "estimated_effort": {
+    "method": "scope (per workflow.md §Tier 1 Track Initialization Rules). NO day estimates.",
+    "child_1": "1 atomic commit (sentinel + 6 migrations) + 1 test + 1 verification",
+    "child_2": "1 atomic commit (handle registry) + 1 test + 1 verification",
+    "child_3": "1 atomic commit (field cache) + 1 test + 1 verification",
+    "phase_4": "1 end-of-campaign report + state + tracks.md"
+  },
+  "verification_criteria": [
+    "VC1: All 3 child tracks SHIPPED (status=completed, current_phase=complete, all phases completed)",
+    "VC2: End-of-campaign report exists with 3 measurements + cumulative reduction",
+    "VC3: Full batched test suite is green (all 11 tiers PASS)",
+    "VC4: 4 audit gates remain clean",
+    "VC5: No new top-level src/<thing>.py files (per AGENTS.md file naming convention)",
+    "VC6: 3 behavioral tests for the 3 SSDL primitives exist and pass"
+  ],
+  "budget_gates": [
+    {
+      "child": "metadata_nil_sentinel_20260624",
+      "baseline": "4.01e22 effective codepaths for Metadata (pre-campaign)",
+      "expected_drop": ">= 10%",
+      "pause_threshold": "drop < 10%",
+      "pause_action": "STOP campaign; report to user; investigate why 6 nil-checks didn't reduce branch count"
+    },
+    {
+      "child": "metadata_generational_handle_20260624",
+      "baseline": "post-child-1 measurement",
+      "expected_drop": ">= 20%",
+      "pause_threshold": "drop < 20%",
+      "pause_action": "STOP campaign; report to user; investigate why lifetime branches didn't collapse"
+    },
+    {
+      "child": "metadata_field_cache_20260624",
+      "baseline": "post-child-2 measurement",
+      "expected_drop": ">= 30%",
+      "pause_threshold": "drop < 30%",
+      "pause_action": "STOP campaign; report to user; investigate why cache lookups didn't reduce branch count"
+    }
+  ],
+  "known_issues": [],
+  "deferred_to_followup_tracks": [
+    {
+      "id": "deferred-same-techniques-other-aggregates",
+      "title": "Apply the 3 SSDL primitives to the other 9 in-scope aggregates (FileItem, CommsLogEntry, HistoryMessage, ToolDefinition, ToolCall, Result, the 3 list-typed, the 3 candidates)",
+      "description": "The 3 SSDL primitives (NIL_METADATA, MetadataHandleRegistry, MetadataFieldCache) are general; the same pattern can be applied to other aggregates. The 4 other dict[str, Any] aggregates (FileItem, CommsLogEntry, HistoryMessage, ToolDefinition, ToolCall) show similar patterns per the parent audit Finding 2.",
+      "track_status": "separate campaign post-this one"
+    }
+  ],
+  "regressions_and_pre_existing_failures": [],
+  "pre_existing_failures_remaining": [],
+  "risk_register": [
+    {
+      "id": "risk-1",
+      "description": "Child 1 doesn't measurably drop the effective-codepaths number",
+      "likelihood": "low",
+      "impact": "Campaign pauses at child 1",
+      "mitigation": "Budget gate catches this; investigate the SSDL math or the audit if drop is 0"
+    },
+    {
+      "id": "risk-2",
+      "description": "Child 2 (generational handle) breaks code that expects raw Metadata",
+      "likelihood": "medium",
+      "impact": "Production code that does `entry['key']` directly fails; need wrapper migration",
+      "mitigation": "The handle is a wrapper; consumers can extract raw value via .value or similar; behavioral test verifies backwards-compat"
+    },
+    {
+      "id": "risk-3",
+      "description": "Child 3 (field cache) cache invalidation is wrong",
+      "likelihood": "medium",
+      "impact": "Stale values returned; subtle bug",
+      "mitigation": "Cache keyed by handle; when underlying value changes, handle generation bumps, invalidating cache entries"
+    },
+    {
+      "id": "risk-4",
+      "description": "Cumulative drop is less than expected",
+      "likelihood": "low",
+      "impact": "Campaign produces smaller improvement than expected",
+      "mitigation": "The campaign's value is in the TECHNIQUE, not the final number; techniques ship, numbers are heuristic"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/conductor/tracks/metadata_ssdl_defusing_20260624/plan.md b/conductor/tracks/metadata_ssdl_defusing_20260624/plan.md
new file mode 100644
index 00000000..de43c831
--- /dev/null
+++ b/conductor/tracks/metadata_ssdl_defusing_20260624/plan.md
@@ -0,0 +1,110 @@
+# Campaign Plan: metadata_ssdl_defusing_20260624
+
+3-child campaign executed sequentially with budget gates. The umbrella plan is intentionally minimal — each child has its own plan. The umbrella tracks the campaign-wide coordination only.
+
+## Phase 1: Child 1 — Nil Sentinel (metadata_nil_sentinel_20260624)
+
+Focus: Establish the sentinel fallback path. Independent of children 2 and 3.
+
+- [ ] Task 1.1: Tier 2 ships child 1 per its own plan.md.
+  - See `conductor/tracks/metadata_nil_sentinel_20260624/plan.md` for the 3-5 tasks.
+- [ ] Task 1.2: Run the budget gate.
+  - `uv run python -c "..."` to compute the new effective-codepaths number for Metadata.
+  - If drop ≥ 10% vs 4.01e22 baseline, proceed to Phase 2.
+  - If drop < 10%, PAUSE and report to user.
+- [ ] Task 1.3: Re-run the full batched test suite.
+  - `uv run python scripts/run_tests_batched.py` → all 11 tiers PASS.
+- [ ] Task 1.4: Capture the post-child-1 measurement in `docs/reports/campaign_measurements_20260624.md` (campaign-wide log).
+
+## Phase 2: Child 2 — Generational Handle (metadata_generational_handle_20260624)
+
+Focus: Wrap Metadata in (index, generation). BLOCKED_BY Phase 1 (the sentinel is the generation-mismatch fallback).
+
+- [ ] Task 2.1: Tier 2 ships child 2 per its own plan.md.
+- [ ] Task 2.2: Run the budget gate.
+  - Re-measure effective-codepaths.
+  - If drop ≥ 20% vs post-child-1 measurement, proceed to Phase 3.
+  - If drop < 20%, PAUSE and report.
+- [ ] Task 2.3: Re-run the full batched test suite.
+- [ ] Task 2.4: Append the post-child-2 measurement to the campaign log.
+
+## Phase 3: Child 3 — Field Cache (metadata_field_cache_20260624)
+
+Focus: Add the cache keyed by handle. BLOCKED_BY Phase 2 (the handle provides the stable cache key).
+
+- [ ] Task 3.1: Tier 2 ships child 3 per its own plan.md.
+- [ ] Task 3.2: Run the budget gate.
+  - Re-measure effective-codepaths.
+  - If drop ≥ 30% vs post-child-2 measurement, proceed to Phase 4.
+  - If drop < 30%, PAUSE and report.
+- [ ] Task 3.3: Re-run the full batched test suite.
+- [ ] Task 3.4: Append the post-child-3 measurement to the campaign log.
+
+## Phase 4: End-of-Campaign Report
+
+Focus: Quantify the cumulative effect.
+
+- [ ] Task 4.1: Write `docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md`.
+  - 3 measurements (post-child-1, -2, -3) + the 4.01e22 baseline.
+  - Total reduction.
+  - The 3 SSDL primitives' locations in `src/`.
+  - Links to each child's TRACK_COMPLETION.
+  - Verdict: did the campaign meet its goal? (Y/N + evidence)
+- [ ] Task 4.2: Update this track's `state.toml` to `status = "completed"`, `current_phase = "complete"`, all 4 phases `completed`.
+- [ ] Task 4.3: Update `conductor/tracks.md` to add the campaign row + the 3 child rows.
+
+## Budget Gate Quick Reference
+
+| Child | Expected drop | If drop < threshold, PAUSE and report |
+|---|---|---|
+| 1: Nil Sentinel | ≥ 10% | Pause; investigate why the 6 nil-checks didn't reduce branch count |
+| 2: Generational Handle | ≥ 20% | Pause; investigate why lifetime branches didn't collapse |
+| 3: Field Cache | ≥ 30% | Pause; investigate why cache lookup didn't reduce branch count |
+
+The thresholds are conservative estimates. Actual drops may be much larger (the heuristic's 4.01e22 is a worst-case upper bound; real numbers may be smaller by orders of magnitude once the techniques are applied).
+
+## Commit Log (Expected, Campaign-Wide)
+
+| Commit | Description |
+|---|---|
+| (from child 1) | `feat(metadata): NIL_METADATA sentinel + 6 nil-check migrations` |
+| (from child 1) | `test(metadata): behavioral test for nil sentinel` |
+| (from child 1) | `conductor(state): metadata_nil_sentinel_20260624 SHIPPED` |
+| (from child 2) | `feat(metadata): generational handle registry` |
+| (from child 2) | `test(metadata): behavioral test for handle lookup` |
+| (from child 2) | `conductor(state): metadata_generational_handle_20260624 SHIPPED` |
+| (from child 3) | `feat(metadata): MetadataFieldCache keyed by handle` |
+| (from child 3) | `test(metadata): behavioral test for cache hit/miss` |
+| (from child 3) | `conductor(state): metadata_field_cache_20260624 SHIPPED` |
+| (campaign) | `docs(reports): TRACK_COMPLETION for metadata_ssdl_defusing_20260624` |
+| (campaign) | `conductor(state): metadata_ssdl_defusing_20260624 SHIPPED` |
+| (campaign) | `conductor(tracks): add campaign + 3 child rows` |
+
+Plus per-task plan-update commits per the workflow.
+
+## Verification Commands (run at end of Phase 4)
+
+```bash
+# VC1: all 3 children SHIPPED
+cat conductor/tracks/metadata_nil_sentinel_20260624/state.toml | grep status
+cat conductor/tracks/metadata_generational_handle_20260624/state.toml | grep status
+cat conductor/tracks/metadata_field_cache_20260624/state.toml | grep status
+
+# VC2: end-of-campaign report
+cat docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md
+
+# VC3: full test suite
+uv run python scripts/run_tests_batched.py
+
+# VC4: 4 audit gates
+uv run python scripts/audit_weak_types.py --strict
+uv run python scripts/generate_type_registry.py --check
+uv run python scripts/audit_main_thread_imports.py
+uv run python scripts/audit_no_models_config_io.py
+
+# VC5: no new top-level src/ files
+git diff master..HEAD --stat -- 'src/*.py' | grep -E '\bsrc/[a-z_]+\.py\b' | sort -u
+
+# VC6: behavioral tests
+uv run pytest tests/test_metadata_nil_sentinel.py tests/test_metadata_generational_handle.py tests/test_metadata_field_cache.py -v
+```
\ No newline at end of file
diff --git a/conductor/tracks/metadata_ssdl_defusing_20260624/spec.md b/conductor/tracks/metadata_ssdl_defusing_20260624/spec.md
new file mode 100644
index 00000000..ca06bed8
--- /dev/null
+++ b/conductor/tracks/metadata_ssdl_defusing_20260624/spec.md
@@ -0,0 +1,147 @@
+# Campaign Specification: metadata_ssdl_defusing_20260624
+
+## Overview
+
+3-child campaign to defuse the `Metadata` aggregate's combinatoric explosion (4.01e22 effective codepaths) via Fleury's SSDL techniques. Each child produces one SSDL primitive, is independently shippable, and is gated by a budget check that re-measures effective codepaths after each child.
+
+The parent audit (`code_path_audit_20260607` / `AUDIT_REPORT.md` Finding 1, CRITICAL) identified 3 specific techniques:
+1. **Nil Sentinel `[N]`** for the 6 nil-check functions
+2. **Generational Handle** wrapping Metadata
+3. **Immediate-Mode Cache `[Q:key] -> [I:FetchCached] -> [T]`** for the 123 field-access sites
+
+The campaign executes them in dependency order: child 1 introduces the sentinel fallback that child 2's generation-mismatch path returns to; child 2's stable identity enables child 3's cache keying.
+
+## Current State Audit (as of master @ 7a9261c4, post-fix_test_failures_20260624 merge)
+
+The audit baseline is captured in `docs/reports/code_path_audit/2026-06-22/AUDIT_REPORT.md`:
+- **Metadata:** 483 producers / 752 consumers / 123 field-access sites (0 typed)
+- **Effective codepaths:** 4.01e22 (sum of 2^branches across 752 consumers)
+- **Branch points:** 3466 across consumer functions
+- **Nil-check functions:** 6 (the `is None` / `== None` / `!= None` detection sites)
+
+The behavioral SSDL test exists at `tests/test_code_path_audit_ssdl_behavioral.py` and uses a synthetic 5-function × 3-if-statements fixture to assert `compute_effective_codepaths` math (5 × 2^3 = 40). The real-Metadata measurement is captured by `src.code_path_audit_ssdl.compute_effective_codepaths(Metadata_profile)`.
+
+## Goals
+
+| ID | Goal | Acceptance |
+|---|---|---|
+| G1 | Child 1 (Nil Sentinel) ships: 6 nil-check functions use sentinel-return | 6 functions refactored; behavioral test for sentinel; 4.01e22 number drops measurably |
+| G2 | Child 2 (Generational Handle) ships: lifetime branches collapse to 1 lookup + 1 generation comparison | Registry in place; 1 lookup benchmark; further effective-codepath drop |
+| G3 | Child 3 (Field Cache) ships: 123 string-keyed `entry.get('key', default)` sites become cache hits | Cache in place; 123 sites benchmarked; further effective-codepath drop |
+| G4 | End-of-campaign report: cumulative effective-codepath measurement vs 4.01e22 baseline | `docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md` written |
+| G5 | All 4 audit gates remain clean | weak_types ≤ 112, type_registry in sync, main_thread_imports clean, no_models_config_io clean |
+
+## Non-Goals
+
+- Touching any aggregate OTHER than Metadata (the audit's other 9 in-scope aggregates + 3 candidates are out of scope; the SSDL primitives established by this campaign can be applied to them in follow-up campaigns)
+- Modifying the audit infrastructure (`src/code_path_audit*.py`); the campaign USES the audit to measure progress but does not change the audit
+- Refactoring the 7-file split (NG3 from `code_path_audit_polish_20260622`); that's a separate refactor track
+- Runtime profiling (the campaign uses the static `branch_count` heuristic; runtime profiling is Track F from the previous menu)
+
+## Per-Child Specs
+
+### Child 1: `metadata_nil_sentinel_20260624` (Nil Sentinel)
+
+**Scope:** Introduce `NIL_METADATA = Metadata(...)` constant with safe defaults. Migrate the 6 nil-check functions (detected by `src.code_path_audit_ssdl.detect_nil_check_pattern`) to sentinel-return: replace `if entry is None: ...` / `if entry == None: ...` / `if entry != None: ...` patterns with `entry = entry or NIL_METADATA` (or the function's equivalent).
+
+**Acceptance:**
+- 6 functions refactored
+- 1 behavioral test (`tests/test_metadata_nil_sentinel.py`): asserts the sentinel is used, asserts the 6 functions no longer have the 3-pattern nil-check branches
+- Budget gate: re-run `compute_effective_codepaths(Metadata_profile)`; if the number drops by < 10%, pause and report
+
+**Why first:** establishes the sentinel that child 2's generation-mismatch path returns to.
+
+### Child 2: `metadata_generational_handle_20260624` (Generational Handle)
+
+**Scope:** Wrap Metadata in `(index, generation)` resolved through a registry. Validation is one comparison: if `metadata.generation != registry.generations[metadata.index]`, return `NIL_METADATA`. Otherwise, the value is valid.
+
+**Acceptance:**
+- `MetadataHandleRegistry` (or equivalent) introduced in a sensible location (likely `src/aggregate.py` or a new sibling module per AGENTS.md §File Naming Convention)
+- Migration: the production `Metadata` value is now wrapped in a handle; lifetime-branch code (e.g., the 3466 branch points that include lifetime checks) collapses to 1 lookup + 1 comparison
+- 1 behavioral test: assert handle lookup is O(1), assert generation mismatch returns sentinel
+- Budget gate: re-run `compute_effective_codepaths(Metadata_profile)`; if the number drops by < 20%, pause and report (the generational handle is expected to produce a larger drop than the sentinel)
+
+**Why second:** builds on child 1's sentinel as the fallback path. Provides a stable identity for child 3's cache keying.
+
+### Child 3: `metadata_field_cache_20260624` (Immediate-Mode Cache)
+
+**Scope:** Introduce `MetadataFieldCache[(handle_id, field_name)] -> value`. Consumers request `(metadata_handle, 'field_name')`, get cached value. The 123 string-keyed `entry.get('key', default)` sites become 123 cache lookups.
+
+**Acceptance:**
+- `MetadataFieldCache` introduced
+- Migration: the 123 field-access sites in `src/` use the cache
+- 1 behavioral test: assert cache hit, assert cache miss with sentinel fallback
+- Budget gate: re-run `compute_effective_codepaths(Metadata_profile)`; if the number drops by < 30%, pause and report (the cache is expected to produce the largest drop)
+
+**Why third:** the cache needs the handle's stable identity (child 2) to use as a key.
+
+## Budget Gate Protocol
+
+After each child commits:
+
+1. **Measure:** run `uv run python -c "from src.code_path_audit import AggregateProfile, ...; from src.code_path_audit_ssdl import compute_effective_codepaths; profile = ...; print(compute_effective_codepaths(profile, 'src'))"`
+2. **Compare:** diff vs prior measurement (or 4.01e22 baseline for child 1)
+3. **Gate:** if drop < expected threshold (10% / 20% / 30% per child), PAUSE the campaign and report to user
+4. **Continue:** if drop ≥ threshold, proceed to next child
+
+The measurement is captured in the child track's TRACK_COMPLETION report and rolled up into the campaign's end-of-campaign report.
+
+## Functional Requirements
+
+### FR1: Each child preserves the existing test suite
+After each child, all 6 VCs from the parent `fix_test_failures_20260624` track remain green: 14 previously-failing tests still pass; no new failures.
+
+### FR2: Each child is independently shippable
+A child can be merged without the other 2 (the campaign gates are forward-looking; a child that meets its budget is shippable on its own).
+
+### FR3: The end-of-campaign report quantifies the cumulative effect
+`docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md` shows: pre-campaign baseline 4.01e22, post-child-1 number, post-child-2 number, post-child-3 number, total reduction.
+
+## Non-Functional Requirements
+
+- NFR1: 1-space indentation (project convention)
+- NFR2: CRLF line endings on Windows
+- NFR3: No comments in source code
+- NFR4: No new pip dependencies
+- NFR5: Per-task atomic commits with git notes
+- NFR6: Each child's `Result[T]` returns for fallible fns (per `conductor/code_styleguides/error_handling.md`)
+- NFR7: The new SSDL primitives are exported from a sensible location; no new top-level `src/<thing>.py` files (per AGENTS.md §File Naming Convention) unless the user explicitly approves
+
+## Architecture Reference
+
+- `docs/reports/code_path_audit/2026-06-22/AUDIT_REPORT.md` — Finding 1 (CRITICAL) and the 3 proposed fixes
+- `src/code_path_audit_ssdl.py:84-100` — `detect_nil_check_pattern` (the function that identifies the 6 nil-check sites)
+- `src/code_path_audit_ssdl.py:39-55` — `compute_effective_codepaths` (the measurement function)
+- `src/code_path_audit.py:271-296` — `CANONICAL_MEMORY_DIM` and `MEMORY_DIM_FILE_HEURISTIC` (where to file new primitives)
+- `conductor/code_styleguides/data_oriented_design.md` — the canonical DOD reference
+- `conductor/code_styleguides/error_handling.md` — the `Result[T]` convention
+- `conductor/code_styleguides/agent_memory_dimensions.md` — the 4 memory dimensions (Metadata is `discussion`)
+
+## Out of Scope
+
+- Aggregates other than Metadata (FileItem, CommsLogEntry, HistoryMessage, ToolDefinition, ToolCall, Result, the 3 list-typed, the 3 candidates) — the SSDL primitives are general but the campaign is Metadata-specific
+- Modifying `src/code_path_audit*.py` (the audit infrastructure)
+- Refactoring the 7-file split
+- Runtime profiling (Track F from the previous menu)
+- Modifying the campaign structure (3 children are fixed; adding a 4th is out of scope)
+
+## Verification Criteria (Definition of Done)
+
+| # | Criterion | Verification command |
+|---|---|---|
+| VC1 | All 3 children SHIPPED | Each child track has `status = "completed"`, `current_phase = "complete"`, all phases `completed` |
+| VC2 | End-of-campaign report exists | `cat docs/reports/TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md` shows the 3 measurements + cumulative reduction |
+| VC3 | Full test suite remains green | `uv run python scripts/run_tests_batched.py` → all 11 tiers PASS |
+| VC4 | 4 audit gates remain clean | weak_types ≤ 112, type_registry in sync, main_thread_imports clean, no_models_config_io clean |
+| VC5 | No new `src/<thing>.py` files created (per AGENTS.md) | `git diff master..HEAD --stat -- 'src/*.py' \| grep -E 'src/[a-z_]+\.py'` returns only the existing `src/` modules; the new SSDL primitives live in existing files |
+| VC6 | Behavioral tests for each child exist and pass | `uv run pytest tests/test_metadata_nil_sentinel.py tests/test_metadata_generational_handle.py tests/test_metadata_field_cache.py -v` → all pass |
+
+## Risks
+
+| # | Risk | Likelihood | Mitigation |
+|---|---|---|---|
+| R1 | Child 1 doesn't measurably drop the effective-codepaths number | low | The 6 nil-checks are documented in AUDIT_REPORT.md; their removal MUST drop the number. If not, the audit or the SSDL math is wrong (separate investigation). |
+| R2 | Child 2 (generational handle) breaks code that expects raw `Metadata` | medium | The handle is a wrapper; consumers can still extract the raw value via `.value` or similar. Behavioral test verifies backwards-compat for the common cases. |
+| R3 | Child 3 (field cache) cache invalidation is wrong | medium | The cache is keyed by `(handle_id, field_name)`. When the underlying value changes, the handle's generation bumps, invalidating all cache entries for that handle. The cache is a write-through thin wrapper. |
+| R4 | The cumulative drop is less than expected (e.g., 4.01e22 → 1e15 instead of 4.01e22 → 1e5) | low | The campaign's value is in the TECHNIQUE, not the final number. The numbers are heuristic; the actual goal is the structural improvement (sentinel, handle, cache). If the techniques ship, the campaign succeeds regardless of the final heuristic number. |
+| R5 | New `src/<thing>.py` files needed for the SSDL primitives | low | Per AGENTS.md, helpers go in the parent module. The new primitives live in `src/aggregate.py` (the parent module for `Metadata`). If the user explicitly approves new top-level files, the campaign can be extended. |
\ No newline at end of file
diff --git a/conductor/tracks/metadata_ssdl_defusing_20260624/state.toml b/conductor/tracks/metadata_ssdl_defusing_20260624/state.toml
new file mode 100644
index 00000000..9ceedeec
--- /dev/null
+++ b/conductor/tracks/metadata_ssdl_defusing_20260624/state.toml
@@ -0,0 +1,67 @@
+# Campaign state for metadata_ssdl_defusing_20260624
+# 3-child campaign; sequential with budget gates.
+# Tier 2 to execute per conductor/workflow.md.
+
+[meta]
+track_id = "metadata_ssdl_defusing_20260624"
+name = "Metadata SSDL Defusing Campaign"
+status = "active"
+current_phase = 0
+last_updated = "2026-06-24"
+
+[parent]
+# Independent campaign (not part of an umbrella)
+
+[blocked_by]
+code_path_audit_20260607 = "shipped"
+
+[blocks]
+# This campaign blocks no other tracks. It is an exploratory campaign.
+
+[child_tracks]
+metadata_nil_sentinel_20260624 = { status = "pending", short_name = "child_1_nil_sentinel" }
+metadata_generational_handle_20260624 = { status = "pending", short_name = "child_2_handle" }
+metadata_field_cache_20260624 = { status = "pending", short_name = "child_3_cache" }
+
+[phases]
+phase_1 = { status = "pending", checkpointsha = "", name = "Child 1: Nil Sentinel (with budget gate >= 10% drop)" }
+phase_2 = { status = "pending", checkpointsha = "", name = "Child 2: Generational Handle (with budget gate >= 20% drop)" }
+phase_3 = { status = "pending", checkpointsha = "", name = "Child 3: Field Cache (with budget gate >= 30% drop)" }
+phase_4 = { status = "pending", checkpointsha = "", name = "End-of-Campaign Report" }
+
+[tasks]
+# Phase 1
+t1_1 = { status = "pending", commit_sha = "", description = "Tier 2 ships child 1 per its own plan.md" }
+t1_2 = { status = "pending", commit_sha = "", description = "Run child 1 budget gate (>= 10% drop); pause if not met" }
+t1_3 = { status = "pending", commit_sha = "", description = "Re-run full batched test suite; verify all 11 tiers PASS" }
+t1_4 = { status = "pending", commit_sha = "", description = "Capture post-child-1 measurement in campaign_measurements_20260624.md" }
+# Phase 2
+t2_1 = { status = "pending", commit_sha = "", description = "Tier 2 ships child 2 per its own plan.md" }
+t2_2 = { status = "pending", commit_sha = "", description = "Run child 2 budget gate (>= 20% drop); pause if not met" }
+t2_3 = { status = "pending", commit_sha = "", description = "Re-run full batched test suite" }
+t2_4 = { status = "pending", commit_sha = "", description = "Append post-child-2 measurement to campaign log" }
+# Phase 3
+t3_1 = { status = "pending", commit_sha = "", description = "Tier 2 ships child 3 per its own plan.md" }
+t3_2 = { status = "pending", commit_sha = "", description = "Run child 3 budget gate (>= 30% drop); pause if not met" }
+t3_3 = { status = "pending", commit_sha = "", description = "Re-run full batched test suite" }
+t3_4 = { status = "pending", commit_sha = "", description = "Append post-child-3 measurement to campaign log" }
+# Phase 4
+t4_1 = { status = "pending", commit_sha = "", description = "Write TRACK_COMPLETION_metadata_ssdl_defusing_20260624.md" }
+t4_2 = { status = "pending", commit_sha = "", description = "Update this state.toml to status=completed" }
+t4_3 = { status = "pending", commit_sha = "", description = "Update conductor/tracks.md with campaign + 3 child rows" }
+
+[verification]
+vc1_all_3_children_shipped = false
+vc2_end_of_campaign_report_exists = false
+vc3_full_batched_suite_green = false
+vc4_audit_gates_clean = false
+vc5_no_new_top_level_src_files = false
+vc6_3_behavioral_tests_pass = false
+
+[measurements]
+# Format: baseline_4.01e22 = sum of 2^branches across all 752 Metadata consumers
+# Populated by Tier 2 as children ship
+pre_campaign = 4.01e+22
+post_child_1 = null
+post_child_2 = null
+post_child_3 = null
\ No newline at end of file