fix(hooks): PreCompact emits bare {} — Claude Code dropped the PreCompact envelope

[mahmoudimus]

What

Claude Code tightened its hook stdout schema: the hookSpecificOutput union no longer has a PreCompact variant, so the previous envelope {"hookSpecificOutput": {"hookEventName": "PreCompact"}} now fails validation:

PreCompact [simba hook PreCompact] failed: Hook JSON output validation failed — (root): Invalid input

The PreCompact render path now emits a bare {} (every top-level field is optional), which is valid under both the old and new schemas. stderr remains the human-visible channel; the export/distill work itself is unchanged.

Changes

• src/simba/harness/adapters/claude.py — the PreCompact branch returns {} unconditionally (never suppressOutput, never a hookSpecificOutput envelope).
• src/simba/hooks/_io.py — docstring carve-out: PreCompact no longer has an envelope variant and never calls into this module.
• Tests re-targeted to the new contract (adapter + pre_compact/streaming/distill suites); the red-first adapter tests reproduce the exact rejected shapes.

Notes

• .codex/hooks.json also registers PreCompact through this same render path; a bare {} is an inert no-op there too.
• The pi bridge posts events to the daemon over HTTP and never consumes this stdout envelope.
• CanonicalResult.suppress_output is still used by the internal hook-canonical debugging surface; intentionally untouched.