docs(refresh): 3 new guides + cross-links from nagent_review

Per the docs Refresh Protocol (conductor/workflow.md), after a
reference/analysis track ships, the affected guides must be updated
to reflect new module structure or new conventions. The nagent_review
track (9cc51ca9) produced a deep-dive + 10 actionable takeaways that
named 3 documentation gaps in /docs. This commit fills them.

3 new guides (1,122 lines total):

1. guide_discussions.md (353 lines) — The Discussion system
   - 23-operation matrix: A1-A7 per-entry + B1-B11 discussion-level
     + C1-C5 undo/redo
   - Take naming convention (<base>_take_<n>), branching, promotion
   - User-managed role list (app.disc_roles)
   - Per-role filter linked to MMA persona focus
   - _disc_entries_lock thread-safety contract
   - Hook API session endpoints
   - Persistence: _flush_to_project, _flush_disc_entries_to_project,
     context_snapshot
   - 9 file:line refs into gui_2.py:3770-4260 + history.py

2. guide_state_lifecycle.md (375 lines) — Undo/redo + reset + state
   delegation
   - HistoryManager + UISnapshot (13 captured fields, 100-snapshot
     capacity, debounced change-detection at render frame)
   - _handle_reset_session (clears 30+ fields, replaces project,
     preserves active_project_path per the 2026-06-08 regression fix)
   - App.__getattr__/__setattr__ state delegation to Controller
   - 4-thread access pattern with 7 lock-protected regions
   - State persistence: in-memory vs project TOML vs config TOML
   - Hot-reload integration
   - Hook API registries (_predefined_callbacks, _gettable_fields)
   - 14 file:line refs into gui_2.py:1140-1170, history.py,
     app_controller.py:3286-3356

3. guide_context_aggregation.md (394 lines) — The aggregate.py
   pipeline
   - 3 aggregation strategies (auto, summarize, full)
   - 7 per-file view modes (full, summary, skeleton, outline,
     masked, custom, none)
   - Full FileItem schema (9 fields + __post_init__ normalizer)
     at models.py:510-559
   - ContextPreset schema and ContextPresetManager
   - Tier 3 worker variant (build_tier3_context with FuzzyAnchor
     re-resolution and focus-file handling)
   - force_full / auto_aggregate short-circuits
   - Cache strategy (static prefix + dynamic history)
   - 23 file:line refs into aggregate.py:36-518 + models.py:909-937

8 existing guides cross-linked to the 3 new guides and to the
nagent_review track:

- guide_gui_2.md           (+ See Also entries for discussions,
                           state lifecycle, context aggregation,
                           nagent_review report)
- guide_app_controller.md  (+ See Also entries for discussions,
                           state lifecycle, context aggregation,
                           nagent_review report)
- guide_context_curation.md (+ new See Also section pointing to
                            context aggregation + nagent_review)
- guide_architecture.md    (+ new See Also section listing all 10
                           guides + nagent_review report)
- guide_ai_client.md       (+ See Also entries for state lifecycle,
                           context aggregation, nagent_review
                           pitfalls #2 and #4)
- guide_mma.md             (+ new See Also section pointing to
                           context aggregation, discussions,
                           nagent_review report §9 + takeaways §3/§10
                           for SubConversationRunner priority)
- guide_models.md          (+ See Also entries for context
                           aggregation, discussions, nagent_review
                           report §6 on FileItem as strongest
                           curation dimension)
- Readme.md                (+ 3 new guide entries in the index
                           table, with one-line summaries)

No code modified. This is documentation only.

Why these 3 guides specifically:

- guide_discussions.md: The discussion system is the user's most
  edited surface. nagent_review's report §3 enumerated 23 operations
  (A1-C5) that previously existed only as scattered file:line refs
  across gui_2.py. A dedicated guide makes the operation matrix
  discoverable.

- guide_state_lifecycle.md: The undo/redo + reset + state delegation
  machinery is architecturally load-bearing but scattered across 4
  files. After nagent_review identified the provider-side history
  divergence as Pitfall #4, the relationship between Manual Slop's
  state and the provider's state needs explicit documentation.

- guide_context_aggregation.md: aggregate.py (518 lines) is the
  most-touched module after ai_client.py but had no dedicated
  guide. nagent_review confirmed it's Manual Slop's strongest
  curation dimension. A dedicated guide makes the 7 view modes
  and 3 strategies discoverable.

The 3 new guides total 1,122 lines and follow the existing
per-source-file deep-dive style (architectural, data-oriented,
state-management-focused).

docs/guide_app_controller.md

@@ -1,6 +1,6 @@
 # `src/app_controller.py` — Headless Orchestrator & State Hub
 
-[Top](../README.md) | [Architecture](guide_architecture.md) | [MMA](guide_mma.md) | [Testing](guide_testing.md)
+[Top](../README.md) | [Architecture](guide_architecture.md) | [Discussions](guide_discussions.md) | [State Lifecycle](guide_state_lifecycle.md) | [Context Aggregation](guide_context_aggregation.md) | [MMA](guide_mma.md) | [Testing](guide_testing.md)
 
 ---
 
@@ -437,7 +437,9 @@ def test_apply_persona(live_gui):
 - **[guide_ai_client.md](guide_ai_client.md)** — How `ai_client` integrates
 - **[guide_api_hooks.md](guide_api_hooks.md)** — The Hook API the controller exposes
 - **[guide_hot_reload.md](guide_hot_reload.md)** — How the controller supports state-preserving reloads
-- **[guide_history.md](guide_history.md)** — Undo/redo (planned, not yet written)
+- **[guide_discussions.md](guide_discussions.md)** — The Discussion system (Takes, branching, `_switch_discussion`, `_branch_discussion`, `_rename_discussion`, `_delete_discussion`, `_flush_disc_entries_to_project`)
+- **[guide_state_lifecycle.md](guide_state_lifecycle.md)** — The `_handle_reset_session` and `_handle_compress_discussion` flows, the `App.__getattr__`/`__setattr__` state delegation pattern, and the `HistoryManager` integration
+- **[guide_context_aggregation.md](guide_context_aggregation.md)** — The `aggregate.py` pipeline that the controller calls per send (per-provider + Tier 3 worker)
 - **`src/presets.py`, `src/personas.py`, `src/context_presets.py`, `src/tool_presets.py`, `src/tool_bias.py`** — Subsystem managers
 - **`src/history.py`** — `HistoryManager`
 - **`src/rag_engine.py`** — `RAGEngine`
@@ -445,3 +447,4 @@ def test_apply_persona(live_gui):
 - **`src/hot_reload.py`** — `HotReloader`
 - **`src/api_hooks.py`** — `HookServer` (uses the controller's registries)
 - **`src/paths.py`** — `PathManager`
+- **[conductor/tracks/nagent_review_20260608/report.md](../../conductor/tracks/nagent_review_20260608/report.md)** — Deep-dive analysis of the controller's per-provider history globals and other state patterns