fix: bound retained AI file-outline memory per repo (APP-4794)

[warp-dev-github-integration]

Description

The AI repo symbol-outline index retains gigabytes of owned Symbol strings in memory.

ai::index::file_outline::build_outline parses every parsable file in a repository in parallel and parse_file_outline allocates owned Strings for each symbol (name, type_prefix, comment). The resulting FileOutlines are collected into Outline.file_id_to_outline and held per repo by RepoOutlines.outlines (app/src/ai/outline/native.rs).

Per-file size is capped (MAX_FILE_SIZE = 3 MB) and per-repo file count is capped (MAX_REPO_FILE_SIZE_LIMIT = 5000), but there is no cap on the cumulative bytes of the retained outline. One outline is kept per detected repo across all working directories, so large repos — and especially multiple indexed repos — grow the index to multiple GB.

Heap profile evidence

A heap profile from Sentry event 981dd4e8127345738eac30598946cff9 (group 7259255054, "Excessive memory usage detected") was unsymbolized on upload; symbolized offline against the build dSYM it showed:

• Process footprint ≈ 10 GB; sampled live heap ≈ 7.09 GiB
• ai::index::file_outline::native::parse_file_outline (cumulative): ~6.0 GiB / 84%, on rayon workers via build_outline
  • native.rs:250 name.to_owned() — 53%
  • native.rs:259 collect_vec() (building Vec<Symbol>) — 30%

This is a distinct facet from the other open outline PRs (#11982 batches parsing to reduce peak memory; #11984 reuses the tree-sitter Parser to reduce fragmentation) — neither bounds the retained outline.

Fix

Track the cumulative approximate heap size of the outlines built so far and stop building new outlines once a generous 256 MiB per-repo budget is exceeded. The index then degrades to a bounded partial outline instead of growing without limit. Typical repos are far below the budget and are unaffected.

• Symbol::approx_heap_size / FileOutline::approx_heap_size estimate retained bytes.
• build_outline accumulates this across rayon workers (AtomicUsize) and skips remaining files once over budget, logging once.

Follow-up (noted in APP-4794): optionally extend the same budget to the incremental Outline::update path.

Linked Issue

• Linear: APP-4794
• Sentry: https://warpdotdev.sentry.io/issues/7259255054/

Testing

• cargo check -p ai --features local_fs
• cargo clippy -p ai --features local_fs --all-targets -- -D warnings
• cargo test -p ai --features local_fs -- index::file_outline — 5 passed (3 new approx_heap_size tests + 2 existing)

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-BUG-FIX: Bound the memory used by AI codebase symbol indexing so very large repositories no longer cause excessive memory usage.

Conversation: https://staging.warp.dev/conversation/d4d630aa-3fbf-42bc-aec0-194a8a1de4f7
Run: https://oz.staging.warp.dev/runs/019f0e38-2fc5-73f7-91a7-7c7af781fbec

This PR was generated with Oz.