feat(hooks): configurable save_interval via config + env var

[rusel95]

😤 The problem

The stop hook fires every 15 messages. Always. No way to change it without editing source code or uninstalling the plugin.

For long coding sessions this is fine. For a quick 3-message task it is noise. For a CI/automation context it is a blocker.

✅ What this does

Makes the interval configurable — via config file or env var:

// ~/.mempalace/config.json
{"hooks": {"save_interval": 30}}

# Or via env var (takes precedence)
MEMPALACE_HOOKS_SAVE_INTERVAL=30   # save every 30 messages
MEMPALACE_HOOKS_SAVE_INTERVAL=0    # disable stop hook entirely

Priority: env var > config file > default (15)

Setting save_interval: 0 disables the stop hook without uninstalling it. Negative values are clamped to 0.

🔑 Key design decision

save_interval controls only the stop hook. The precompact hook is independent (see PR #1346). Disabling periodic saves does not disable the last-chance save before context compression.

🧪 Tests

All 104 existing hook and config tests pass.

python -m pytest tests/test_hooks_cli.py tests/test_config.py -q
104 passed

Closes #494.

[rusel95]

✅ End-to-end testing completed

Verified against the real MempalaceConfig class and hook_stop() function — no mocks for the config path.

Tests verified:

• Default interval = 15 ✅
• MEMPALACE_HOOKS_SAVE_INTERVAL=50 → interval = 50 ✅
• MEMPALACE_HOOKS_SAVE_INTERVAL=0 → hook disabled ✅
• MEMPALACE_HOOKS_SAVE_INTERVAL=-5 → clamped to 0 ✅
• Config file {"hooks": {"save_interval": 30}} → interval = 30 ✅
• Independence: save_interval=0 does NOT affect precompact ✅

python -m pytest tests/test_hooks_cli.py tests/test_config.py -v
104 passed in 0.65s

Full suite: 0 regressions.

[igorls]

Thanks for this contribution, and apologies for the slow turnaround.

develop has moved a fair way since this was opened and the branch no longer merges cleanly. If you're still interested in landing it, could you rebase onto current develop? Once it merges cleanly and CI is green I'll get it reviewed for the 3.8.0 cycle.

If you'd rather not pick it back up, no problem at all — just say so and I'll close it out, and thanks either way for taking the time to send it.