The long-lived MCP server ran the full index pipeline in-process on two
background paths -- the session auto-index (autoindex_thread, mcp.c) and the
watcher re-index (watcher_index_fn, main.c). The parallel pipeline's worker
threads abandon their mimalloc pages at thread exit, and mimalloc v3 defaults
page_reclaim_on_free=0, so those pages are never reclaimed when the main thread
later frees their blocks (mi_collect cannot touch abandoned pages either). RSS
then ratchets across re-index cycles and never comes back down (#832).
The index_repository tool path already avoided this by running the index in a
supervised worker subprocess: on child exit the kernel reclaims 100% of the
child's RSS. Route the two background paths through that same supervised runner:
- supervisor_invalidate_store() is now NULL-safe (the watcher path has no MCP
server / cached store).
- New static index_run_supervised_path() builds {"repo_path": root} and reuses
the existing spawn + skip-and-continue recovery loop (no duplication). New
public cbm_mcp_index_run_supervised_path() is the srv-less entry main.c calls.
- autoindex_thread and watcher_index_fn gate on cbm_index_supervisor_should_wrap():
supervised on a marked host with the kill switch off, else fall through to the
unchanged in-process pipeline (kill switch / spawn-failure degrade). The
watcher keeps its non-blocking try_lock gate + g_shutdown check exactly; the
lock still serialises re-indexes. cbm_mem_collect() stays on the in-process
branch only.
Also fold in the in-process allocator fallback: cbm_mem_init sets
mi_option_page_reclaim_on_free=1, restoring v2 behaviour so any path that stays
in-process (kill switch, degrade, embedders) also reclaims abandoned worker
pages. The subprocess is the primary cure (child exit returns RSS every cycle);
this is the fallback.
Tests: a deterministic gating guard (test_mcp.c) proves the background paths now
spawn a worker child and index the fixture (RED when routed in-process:
spawn_count unchanged; GREEN after). The test-runner acts as a real in-process
worker when spawned as `cli --index-worker` (public APIs only, no production
seam). A non-gating prod-binary RSS reproduction (tests/repro/issue832_rss.py)
shows the supervised server flat at ~10 MB vs ~131 MB in-process.
Scope: JobObject, the #841 spurious-trigger fix, retention caps, budget tiering
and the backpressure busy-spin are follow-ups.
Refs #832, #841.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
