🐛 fix: raise LMDB mapsize cap 8GB→16GB + PersistentEmbeddingCache auto-resize on MDB_MAP_FULL (#189)

[flupkede]

Summary

Fixes the fatal MDB_MAP_FULL: Environment mapsize limit reached crash on large corpus indexing (#189).

Two complementary changes:

1. Raise the LMDB mapsize cap from 8 GB → 16 GB default, with an env-var override escape hatch.
2. Auto-resize PersistentEmbeddingCache on MDB_MAP_FULL — the cache LMDB was the remaining failure surface after VectorStore::build_index already had this fix; the cache's own put/put_batch paths still aborted on a full map.

Root cause

Two LMDB environments share the process, and only one of them could grow past its cap on MDB_MAP_FULL:

• VectorStore::build_index already had a resize-retry loop.
• PersistentEmbeddingCache::put / put_batch did not — a full cache map was a hard crash.

On top of that, the global MAX_LMDB_MAP_SIZE_MB cap (8 GB) was too small for the repro in #189, so even the resize-capable paths hit the ceiling.

Changes by stage

• Stage 1 (7a58e78) — src/constants.rs, src/vectordb/store.rs
  • Raise MAX_LMDB_MAP_SIZE_MB 8 GB → 16 GB.
  • New max_lmdb_map_size_mb() accessor with env override CODESEARCH_MAX_LMDB_MAP_SIZE_MB (clamped to ≥ 1024 MB; fail-fast on parse error).
  • Route all 5 vector-store cap comparisons through the accessor (no logic change, single source of truth).
• Stage 2 (89244a1) — src/embed/cache.rs
  • Add MDB_MAP_FULL auto-resize retry loops to PersistentEmbeddingCache::put / put_batch, mirroring the existing VectorStore::build_index pattern.
  • Persist the grown mapsize across restarts; &self receiver preserved (no API churn).
• Stage 3 (e58e225) — src/embed/cache.rs
  • 3 tests pinning resize-on-full, persist-after-grow, and reopen-with-persisted-mapsize. Defect-injection verified by reviewer.
• Post-stage (116176c) — src/constants.rs
  • Lower the cap 32 GB → 16 GB per user direction: 16 GB is ample for the mapsize fatal crash #189 repro, and the env override remains the escape hatch for any larger corpus.

Escape hatch

# Override the mapsize cap (MB), e.g. 32 GB for a very large corpus
export CODESEARCH_MAX_LMDB_MAP_SIZE_MB=32768

Clamped to a minimum of 1024 MB; a non-integer value fails fast at startup rather than silently falling back.

Validation

All green on push (QC gate):

• cargo fmt --all -- --check
• cargo check --all-targets
• cargo clippy --all-targets -- -D warnings
• cargo test --lib --bins — 558 passed / 0 failed

Reviews

All 4 stages reviewed individually (4× PASS, zero Critical / zero Important findings).

Files changed

File	Delta	What
src/constants.rs	+50 / -3	mapsize cap, accessor + env override
src/vectordb/store.rs	+6 / -13	route caps through accessor
src/embed/cache.rs	+333 / -0	auto-resize + persist + 3 tests

Closes #189

Note: in this develop-based gitflow, Closes #189 resolves when the change reaches master (the release merge), not on the merge into develop. The trailer is included for traceability either way.