fix(tier2-sandbox): add git stash* and git clean -fd* to all 3 ban layers; spell out timeline-is-immutable principle

ROOT CAUSE: Tier 2 used 'git stash' during the cruft_elimination_20260627
track execution and corrupted the user's in-progress files. The user
explicitly stated: 'if an agent fucks up, their tendency to want to revert
is not correct and instead they must live with the timeline and just do
corrections with a new commit. They can grab artifacts, code, etc, from
old commits but they cannot reset to that.'

This commit adds HARD BANs on git stash* and git clean -fd* at 3 layers
(per the existing 3-layer defense model documented in
conductor/tier2/agents/tier2-autonomous.md):

LAYER 1: AGENTS.md
- Added new HARD BAN: 'git stash* (any form: git stash, git stash pop,
  git stash apply, git stash drop, git stash clear) is FORBIDDEN.
  Stashing inverts the safety net of the working tree'

LAYER 2: conductor/tier2/opencode.json.fragment (Tier 2 autonomous)
- Added 'git stash*', 'git stash pop*', 'git stash apply*',
  'git stash drop*', 'git stash clear*', 'git clean -fd*', 'git clean -fdx*'
  to BOTH the top-level permission.bash deny list AND the
  agent.tier2-autonomous.permission.bash deny list
- Also added 'git revert*' (was missing from fragment; already banned in prompt)
- These are now HARD DENIED at the OpenCode permission layer; the agent
  cannot run them even if it tries

LAYER 3: conductor/tier2/agents/tier2-autonomous.md
- Added 'git stash* (any form)' to the Hard Bans list
- Added 'THE TIMELINE-IS-IMMUTABLE PRINCIPLE' section spelling out
  exactly what to do when you fuck up:
  - When you make a wrong commit, write a NEW commit that fixes it
  - The git history is immutable on this branch
  - You CAN grab artifacts from old commits via 'git show <sha>:<path> > <new-path>'
  - You CANNOT reset the branch HEAD to an old commit
  - 'git revert', 'git reset --hard', 'git reset --soft', 'git stash' are
    all attempts to rewrite history and BANNED
  - Correct pattern: pause, read the actual file, write a forward
    corrective commit with a commit message that explains the fix

This addresses the root cause of the 2026-06-27 cruft_elimination
corruption. Future Tier 2 autonomous runs will be blocked from running
git stash* at 2 layers (OpenCode permission deny + Tier 2 prompt hard
ban list) and reminded at the agent-prompt layer (THE TIMELINE-IS-
IMMUTABLE PRINCIPLE section).

AGENTS.md

@@ -57,6 +57,7 @@ The 14 deep-dive guides under `docs/` (`guide_architecture.md`, `guide_ai_client
 - `set_file_slice` IS valid for multi-line content. The agent must verify the exact byte offsets with `get_file_slice` first, copy the line text character-for-character (including whitespace and EOL), and check whether the edit changes a public contract (function signature, yield shape, return type) that other code depends on. See `conductor/edit_workflow.md` for the full contract.
 - Do not use `git restore` while a user is mid-conversation without first confirming the desired state
 - HARD BAN: `git restore`, `git checkout -- <file>`, `git reset` are FORBIDDEN without explicit user permission in the same message. They destroyed user in-progress src/* edits twice in one session (2026-06-07). If you think you need one, ASK FIRST.
+- HARD BAN: `git stash*` (any form: `git stash`, `git stash pop`, `git stash apply`, `git stash drop`, `git stash clear`) is FORBIDDEN. Stashing inverts the safety net of the working tree: a `git add .` then `git stash` then "fresh start" pattern is exactly how Tier 2 corrupted files in the 2026-06-27 `cruft_elimination_20260627` track. The user explicitly stated "I hate when people fuck with my commits" — stashing throws away the user's in-progress edits silently. If you think you need a stash, you don't — use a NEW BRANCH or a WORKTREE instead. Tier 2 sandbox enforces this via `conductor/tier2/opencode.json.fragment` bash deny rules.
 - **HARD BAN: Day estimates in track artifacts (Tier 1).** Do NOT include day / hour / minute estimates in spec.md, plan.md, metadata.json, or any other track artifact. Day estimates are inaccurate noise; Tier 2 capacity is bounded by attention, not time. Measure effort by **scope** (N files, M sites, N tasks). The user / Tier 2 agent decides the actual pacing. See `conductor/workflow.md` §"Tier 1 Track Initialization Rules" for the full rule, replacement patterns, and rationale. (Added 2026-06-16 per user feedback: "Day estimates are inaccurate. Tier-2s can only do so much in a single track and there is no way in hell its going to be 'DAYS'.")
 - **HARD BAN: Opaque types in non-boundary code (added 2026-06-25).** LLMs default to `dict[str, Any]`, `Any`, `Optional[T]`, `hasattr()` polymorphism, and `.get('field', default)` because that's idiomatic Python training data. **All of these are BANNED in non-boundary code.** Use typed `@dataclass(frozen=True, slots=True)` with explicit fields; use `Result[T]` + `NIL_T` sentinels instead of `Optional[T]`; use direct attribute access instead of `.get()`. The ONLY place `dict[str, Any]` is allowed is the literal wire boundary (TOML/JSON parse functions); 2-3 functions per file. See `conductor/product-guidelines.md` "Core Value", `conductor/code_styleguides/data_oriented_design.md` §8.5 (The Python Type Promotion Mandate), `conductor/code_styleguides/python.md` §17 (LLM Default Anti-Patterns), and `conductor/code_styleguides/type_aliases.md` for the canonical mandates. User direction 2026-06-25: "I want the closest thing to c11/odin/jai in a scripting language... metadata should not be a dict[str, any]."