fix(hooks/precompact): unblock /compact and auto-compact

[vasyl-pavlyuchok]

Problem

The PreCompact hook always ends up returning a block decision, preventing both /compact (manual) and auto-compact from working for any user installing this plugin.

The current upstream hook routes through:

run_mempalace_hook --hook precompact --harness claude-code

Which calls mempalace hook run --hook precompact --harness claude-code, and that path returns block. Net effect: no user can compact while this plugin is active.

Fix

Have the hook return {"decision": "allow"} directly so compaction proceeds.

Session saving is NOT affected — it goes through the Stop hook (separate path), which continues to work as designed.

Verification

Tested in production VPS Claude Code environment:

• /compact (manual) now works ✓
• Auto-compact at context threshold now works ✓
• Session saving via Stop hook unaffected ✓
• MemPalace MCP server continues responding correctly ✓

Notes for maintainers

If the original blocking behavior was intentional (e.g. to enforce session save first), please consider an alternative implementation that allows compaction and triggers save — current behavior just blocks all compaction silently, which surprises users.

This patch takes the minimal-impact approach. Happy to iterate on a more nuanced solution if preferred.

[mvalentsev]

This wouldn't merge as-is, for reasons that show up clearly against
develop tip:

1. The premise -- that mempalace hook run --hook precompact returns
   block -- doesn't match the current code. mempalace/hooks_cli.py
hook_precompact() ends with _output({}) after mining the
   transcript and palace synchronously. Empty JSON, not block. That
   was the fix(hooks): stop precompact hook from blocking compaction (#856, #858) #863 fix, merged 2026-04-15 (in v3.3.1+, published
   2026-04-18). If /compact is failing for you, you're likely on a
   pre-3.3.1 install -- bumping to v3.3.4 or current develop should
   make it work without touching the hook script.

2. Side effect of the patch: it bypasses the _ingest_transcript and
   _mine_sync calls the Python path runs synchronously. That is the
   reason the PreCompact hook exists -- capture transcript and project
   mine before compaction loses the tool-output buffer. The Stop hook
   save path is separate and won't cover this.

3. Minor: {"decision": "allow"} is not a documented value for the
   top-level decision field per
   https://code.claude.com/docs/en/hooks.md -- only "block" is. In
   practice Claude Code ignores the unknown value and proceeds, but
   fix: replace invalid 'decision: allow' with {} in hooks (closes #872) #885 (closes bug: hooks use invalid decision value "allow" — should be "approve" #872) specifically cleaned this up to use {}. The
   patch reintroduces the same spec-invalid form.

If /compact is genuinely still broken against develop tip, that
would be a fresh bug worth tracking with the version + repro steps.

[igorls]

Thanks! The precompact hook on develop already ends with an allow decision (since #863); this change would regress precompact mining. Closing as superseded.