Summary

• PR-B fixup that ships independently of PR-D C2's mm context update work.
• installed_at was captured before copy_tree_atomic, leaving freshly installed files with mtimes potentially later than the recorded installed_at. ADR-0008 PR-D's mtime > installed_at dirty check (Invariant 2) would then false-positive on the install's own writes under any non-trivial copytree latency.
• Move capture to the lockfile-upsert boundary (after copy completes) so mtime <= installed_at holds for fresh installs by construction.

Why standalone

C2 (mm context update + dirty detection) consumes this invariant in its is_asset_dirty() classifier. Splitting the fixup into its own PR keeps that change reviewable as a real PR-B bug fix, independent of C2's much larger surface (update CLI, --all cross-project, .bak semantics).

No user-visible behavior change today; the lockfile semantic is tightened so the upcoming dirty check is sound.

Test plan

• New regression test test_installed_at_after_all_writes: install a multi-file skill (4 files across 3 subdirs), walk dest, assert parsed installed_at >= max(dest mtimes) within 1ms slack.
• Existing 19 install tests pass unchanged (packages/memtomem/tests/test_context_install.py).
• Adjacent suites pass: test_context_install_widening.py, test_lockfile.py.
• Full CI filter uv run pytest -m "not ollama" — 3476 passed, 46 deselected.
• ruff check + ruff format --check — green.

Series

Part of ADR-0008 wiki layer:

• ✓ feat(wiki): PR-A — wiki scaffold (~/.memtomem-wiki, mm wiki init/list, ADR-0008) #622 PR-A — wiki scaffold
• ✓ feat(context): PR-B — mm context install skill + lockfile + concurrency #623 PR-B — mm context install + lockfile + concurrency
• ✓ feat(context): PR-C — wiki override + agent/command install widening (ADR-0008) #624 PR-C — wiki override + agent/command install widening
• ✓ feat(context): fan-out override application sites (PR-C carry-forward, ADR-0008 PR-D-prep) #627 PR-D-prep — fan-out application sites
• ✓ feat(context): PR-D C1a — activate agents/commands override + render lift (ADR-0008) #628 PR-D C1a — gate flip + render lift
• ✓ feat(context): PR-D C1b — mm wiki {agent,command} override CLI mirror (ADR-0008) #629 PR-D C1b — mm wiki {agent,command} override CLI mirror
• ➜ this PR — installed_at fixup (C2 prereq)
• (next) PR-D C2 — mm context update + dirty detection

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