feat(memdir): port the Searching-past-context prompt section; keybindings placeholder truth

[ericleepi314]

Summary

Small-folder closes from the get-parity-by-folder sweep — memdir/ (one live gap ported) + keybindings/ (placeholder housekeeping). Five folders were dispositioned in this batch (keybindings/, memdir/, migrations/, moreright/, native-ts/ — docs in my-docs/get-parity-by-folder/); this PR carries the two code changes that fell out.

MEMDIR-1 — the "Searching past context" prompt section. The critic caught a flag misread in my close: I verified GrowthBook call-site default args, but the vendored stub's _openBuildDefaults table sets tengu_coral_fern true — so the reference build emits buildSearchingPastContextSection (memdir.ts:375-407) into every user's memory prompt, and Python's builders omitted it (with load_memory_prompt live in prompt assembly, the omission reached every system prompt). Ported as always-emit: build_searching_past_context_section in src/memdir/memdir.py — Grep-tool invocation forms (this port always ships the Grep tool; TS's shell-grep branch covers ant-native/REPL modes it doesn't have), memory-dir *.md search + the port's saved-session store (~/.clawcodex/sessions/ *.json) as the transcript-search target. Wired at both live TS call sites: build_memory_lines tail (memdir.ts:263) and the combined team prompt after extra guidelines (teamMemPrompts.ts:96). The third TS site (:366) is the KAIROS daily-log builder — deferred with its mode, deliberately not wired. isExtractModeActive (also _openBuildDefaults-ON) is reclassified in the gap doc as a deferred feature with an owner (query/stop-hooks docket), not a memdir residual.

keybindings/ housekeeping. src/keybindings/__init__.py's docstring pointed at src/tui/keybindings.py — deleted with the Textual TUI in the UI-consolidation (#566) — and a superseded plan. Restated to the current truth (defaults live in the kept ui-tui client; the customization gate resolves false in open builds — key absent from _openBuildDefaults). Comment-only; the placeholder stays load-bearing for reference_data snapshots.

Methodological note recorded in the docs: per-flag _openBuildDefaults consultation is now on the sweep's verification checklist (resolver, not call-site default) — the same table proved one flag ON (coral_fern → this port) and one absent (herring_clock → the existing env-var substitution stands).

Verification

• 4 new pins in tests/test_memdir_memdir.py: section content (both Grep forms + the narrow-terms line), build_memory_lines ends with the section, build_memory_prompt keeps it before the MEMORY.md block (matching TS :293 composition), combined prompt ends with it exactly once.
• memdir suites 43 green; test_porting_workspace (placeholder pin) green.
• Full suite at the 6-failure baseline (7766 passed).
• Critic loop: five dispositions reviewed (2 APPROVE first-pass, 3 REVISE→fixed); implementation reviewed on the revision round.

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