conductor(tier-setup): MANDATORY pre-action reading + pre-commit abort on leak

ROOT CAUSE (post-mortem at docs/reports/TIER2_MCP_REGRESSION_20260624.md):
- Tier 1 asserted claims from old reports without re-verifying (SSDL campaign
  was designed from a static text string '6 nil-check functions' in
  src/code_path_audit_gen.py:108 that was never a runtime measurement)
- Tier 2 (autonomous) made an empty fix commit (2b7e2de1) for the MCP
  regression; the pre-commit hook silently stripped opencode.json +
  mcp_paths.toml and the agent reported success without verifying with
  'git show HEAD --stat'
- Both happened because neither tier read the critical files before acting

THE FIX (this commit):

1. .agents/agents/tier1-orchestrator.md: add MANDATORY pre-action reading
   list (6 files: AGENTS.md, conductor/workflow.md, current track spec/plan,
   the 3 code_styleguides). Reference the 2026-06-24 SSDL failures.

2. .agents/agents/tier2-tech-lead.md: add MANDATORY pre-action reading list
   (8 files: AGENTS.md, workflow.md, edit_workflow.md, the githooks
   forbidden-files.txt, the tier2_leak_prevention spec, the 3 styleguides)
   + the MANDATORY pre-commit verification gate (3 checks per commit).

3. .agents/agents/tier3-worker.md: add 4-file read list (AGENTS.md, task
   spec, relevant styleguide, the actual code being modified). Tier 3 doesn't
   need the full 8-file list — Tier 2's task spec is the contract.

4. .agents/agents/tier4-qa.md: same 4-file read list (analysis context).

5. conductor/tier2/agents/tier2-autonomous.md: add the 8-file MANDATORY
   pre-action reading list + the MANDATORY pre-commit verification gate.

6. conductor/tier2/commands/tier-2-auto-execute.md: add the 8-file list
   to the pre-flight section (step 0).

7. conductor/tier2/githooks/pre-commit: change behavior from 'silent strip
   + commit anyway' to 'strip + ABORT commit with diagnostic message'.
   The previous behavior led to empty commits (the 2026-06-24 regression).
   The agent MUST investigate the leak before retrying the commit.

ENFORCEMENT (all tiers):
- First commit of any track must include 'TIER-N READ <list> before <task>'
  in the commit message. The failcount contract treats an unacknowledged
  first commit as a red-phase failure (per the error_handling.md Rule #0
  precedent).

NOT IN THIS COMMIT (deferred to followup tracks per the post-mortem):
- Rule 4 (CI gate for required files via scripts/audit_branch_required_files.py)
- AGENTS.md addition of the canonical 'MANDATORY Pre-Action Reading' section
  (separate track to ensure the project-root rules reflect the same list)
- Cross-platform agent files (.opencode/, .claude/, .gemini/) — those are
  generated from the canonical .agents/agents/ files; this commit updates
  the canonical sources.

7 files modified, 109 insertions, 6 deletions.

conductor/tier2/githooks/pre-commit

@@ -73,11 +73,13 @@ if [ ! -s "$TMPFILE" ]; then
  exit 0
 fi
 
-echo "Tier 2: removing sandbox-only files from staging" >&2
-echo "(these files belong in the main repo, not in tier-2 commits):" >&2
+# Auto-unstages the leak. Then ABORTS the commit so the agent MUST investigate
+# before retrying. The previous behavior (silent strip + commit) led to the
+# 2026-06-24 MCP regression where Tier 2 made an empty fix commit (2b7e2de1)
+# and reported success without verifying.
 while IFS= read -r f; do
  [ -z "$f" ] && continue
- echo " - $f" >&2
+ echo " - unstaging: $f" >&2
  # `git rm --cached` works on tracked files (unstages modifications)
  # AND on newly-added files (unstages the addition, file becomes
  # untracked again). NOT `git restore` (banned in sandbox).
@@ -90,7 +92,16 @@ while IFS= read -r f; do
 done < "$TMPFILE"
 
 echo "" >&2
-echo "Commit will proceed without these files. To inspect what was" >&2
-echo "removed, run: git status" >&2
+echo "Tier 2: COMMIT ABORTED — sandbox file leak detected." >&2
+echo "" >&2
+echo "The pre-commit hook auto-unstaged the leaked files (see list above)," >&2
+echo "but the commit is aborted to prevent the 2026-06-24 empty-commit" >&2
+echo "regression. Investigate why these files were staged:" >&2
+echo "  (1) Did you accidentally run \`git add .\`? Use \`git add <specific_files>\`" >&2
+echo "  (2) Did the files leak from setup_tier2_clone.ps1? Check \`git status\`." >&2
+echo "  (3) Are the files intentionally part of your work? Re-stage them with" >&2
+echo "      \`git add <path>\` after confirming they're NOT in forbidden-files.txt." >&2
+echo "" >&2
+echo "Re-attempt the commit after resolving the leak." >&2
 
-exit 0
+exit 1