fix(state): honour HERMES_DISABLE_FTS_TRIGRAM to skip CJK index

[bilawalriaz]

What & why

Closes #22478.

The CJK trigram FTS5 index is currently created unconditionally when FTS5 is available. On large histories it accounts for the majority of state.db size — the user-reported numbers in #22478 show messages_fts_trigram alone at 247 MB (49% of a 505 MB DB), and the trigram index is 2.2× larger than the porter-stemmer index that indexes the same data.

The docstring on optimize_fts() already promised an HERMES_DISABLE_FTS_TRIGRAM opt-out, but no code path actually read the variable — it was dead documentation. This PR wires the gate up everywhere it matters.

Changes

• Add _trigram_fts_disabled() helper reading HERMES_DISABLE_FTS_TRIGRAM (accepts 1/true/yes/on, case-insensitive, whitespace-trimmed).
• Split _FTS_TRIGGERS into _PORTER_FTS_TRIGGERS and _TRIGRAM_FTS_TRIGGERS. _drop_fts_triggers still iterates the full union so a user who flips the var back on doesn't leave stale triggers on disk.
• Gate the v10 and v11 schema migrations, the normal-startup schema creation, _rebuild_fts_indexes, and _fts_trigger_count on the helper.
• search_messages() now falls through to the LIKE-based CJK path when the trigram table is absent, so English / short-CJK / mixed queries still work after disabling the index.
• New TestTrigramFtsDisabled class with 7 tests covering: env-var truthy parsing, default behaviour, table non-creation, trigger non-creation, English search still functional, and optimize_fts() returning 1 (porter only) instead of 2.

How to test

# 1. Confirm the new behaviour
HERMES_DISABLE_FTS_TRIGRAM=1 scripts/run_tests.sh tests/test_hermes_state.py -- -v -k TestTrigramFtsDisabled

# 2. Regressions on the FTS path
scripts/run_tests.sh tests/test_hermes_state.py
scripts/run_tests.sh tests/test_hermes_state.py tests/tools/test_session_search.py

To verify end-to-end space reclamation on a real DB:

cp ~/.hermes/state.db ~/.hermes/state.db.pre-trigram
echo "HERMES_DISABLE_FTS_TRIGRAM=1" >> ~/.hermes/.env
hermes   # trigram table gets dropped on startup
sqlite3 ~/.hermes/state.db "VACUUM"

Platforms tested

• Linux (Ubuntu)

Notes

• Pre-existing failure in tests/agent/test_auxiliary_client.py (8 tests) is unrelated and reproduces on main before this branch.
• No new dependencies. import os added to hermes_state.py.

[teknium1]

Thanks for tackling the documented state.db bloat; the reports in #22478 substantiate the storage cost of the trigram index.

This automated hermes-sweeper review is closing the PR under the standing configuration policy:

• Current main still creates the optional CJK trigram index in hermes_state.py:1661-1671, so the underlying problem is real.
• This PR's public mechanism is the new non-secret behavioral flag HERMES_DISABLE_FTS_TRIGRAM (commit e2e0a8628aec).
• AGENTS.md:102-107 reserves .env / HERMES_* variables for credentials and requires behavioral feature flags to be exposed through config.yaml.

Please feel free to re-scope the opt-out as a config.yaml setting, carrying forward the current migration, trigger-repair, existing-index cleanup, re-enable/backfill, and CJK LIKE-fallback coverage.

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Closed as not-planned per standing maintainer policy (env-var-for-config). This is a design-direction decision, not a code-quality judgment.

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Closed as not-planned per standing maintainer policy (env-var-for-config). This is a design-direction decision, not a code-quality judgment — see the Contribution Rubric in AGENTS.md for what the project is looking for. If you believe this policy was misapplied to your change, comment here and a maintainer will take a look.