session: the uv-tool repair belongs to the hook, not the bootstrap

[Jammy2211]

Summary

Two halves of the 2026-08-27 mobile-workflow pass that were, by construction, only half-rolled-out — the session that shipped them could attach only two of the four organs. Closes the second half here; the first half (Heart and Hands opting into the generated remote-session block) ships in their own PRs.

repair_uv_tools shipped in scripts/session_bootstrap.sh. That is the wrong home. The bootstrap is what a multi-repo session runs, because that session registers no SessionStart hook and has no other door. A single-repo session is the mirror image: the hook fires, nothing calls the bootstrap. It got leg 2's breakage — the /usr/local/bin/python3 wrapper that every uv tool env symlinks to — and none of the repair, so mypy, flake8, black, poetry and pyright all died with ModuleNotFoundError naming themselves, in the ordinary single-repo case.

Moved into policy/session_start_hook.sh as leg 3b, called right after retool_uv_tools. Two paths reach that breakage, not one: leg 3 rebuilds a 3.11 tool and hands the new env the hijacked path, and leg 2 separately breaks every pre-existing tool env that already pointed there and that leg 3 skips (is_py312 … && continue). Running after leg 3 covers both, because leg 2 runs before it.

API Changes

None — no public Python API is touched. Two shell contracts change, both internal to the session machinery:

• policy/session_start_hook.sh gains a --repair-uv-tools argv seam (previously took no arguments) and calls repair_uv_tools in its main flow.
• scripts/session_bootstrap.sh no longer defines repair_uv_tools; its own --repair-uv-tools seam and its trailing call now forward to the hook as subprocesses. The --check leg is unchanged.

See full details below.

Test Plan

• python3 -m pytest -q in PyAutoMind — 271 passed
• The four new tests fail on exactly the bug when the flow call is removed:
  assert '/tmp/…/session' == '/tmp/…/tools/widget'
• repos_sync.py --check --root <four-organ scope> — all 14 legs OK
• All four organs' hook copies byte-identical to the canonical
• Sibling suites green: PyAutoBrain 584, PyAutoHeart 656, PyAutoHands 430

Hardening the move required

The hook runs set -euo pipefail; the bootstrap ran set -u only. Three things would have failed the whole session start, silently, in a script whose contract is that every leg "degrades to a logged warning":

• base="$(… 2>/dev/null)" — a failing command substitution in an assignment aborts under set -e
• the post-repair prefix="$(…)" — same
• ln -sfn itself, on an unwritable tools dir — now warns and continues

Scope: this does not clean up the long tail

write_session_hooks iterates the whole manifest, so the hook is generated into 34 repos, not four. Thirty of those copies are a pass behind and two carry none at all — a state that predates this PR and that no gate sees, because firewall_gate.yml checks out exactly the four organs and skips absent repos. Heart sees it (manifest drift: session-start hooks (generated) — 34 mismatch(es)), CI does not.

This PR regenerates the four organs — the set CI actually gates — and leaves the count where it found it. The propagation is filed separately as draft/maintenance/organs/session_hook_reaches_only_four_of_thirty_four_repos.md, since it would mean PRs against every library, workspace, HowTo and assistant repo.

Full API Changes (for automation & release notes)

Added

• policy/session_start_hook.sh --repair-uv-tools — runs leg 3b alone, without a session start. Honours PYAUTO_UV_TOOLS_DIR and PYAUTO_SESSION_VENV.
• repair_uv_tools() in policy/session_start_hook.sh (leg 3b), called from the main flow after retool_uv_tools.

Removed

• repair_uv_tools() from scripts/session_bootstrap.sh — moved, not deleted.

Migration

• None for callers. bash PyAutoMind/scripts/session_bootstrap.sh --repair-uv-tools still works and still repairs; it now forwards to the hook.

Closes part 2 of #360.

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