Document the stack size local test runs need

[EnRaiha]

Why

Rust spawns threads at 2 MiB. Debug-profile test binaries overflow that default: at the default the native suite aborts with SIGABRT (measured on this branch), at 32 MiB it passes. CI already carries the fix — .github/workflows/test.yml:135 sets RUST_MIN_STACK: "33554432" for the test job, matching the margin nodedb-test-support/src/core_loop_runner.rs:7 documents — and a local run without the variable does not.

.cargo/config.toml was the first attempt and is removed per review: .gitignore:111 ignores .cargo/ because that file is each contributor's local override ([build] jobs, [patch]); tracking it turns every existing local copy into a merge conflict. The value lives on the documented command line instead.

What changed

CONTRIBUTING.md, "Running tests" block — one comment sentence and the command:

# Run the full test suite
# Debug-profile test binaries overflow the 2 MiB thread default; 32 MiB is the value CI sets.
RUST_MIN_STACK=33554432 cargo nextest run --all-features

No config file. No product change.

Wording

RUST_MIN_STACK is not a floor. It replaces the default stack size for every std::thread::spawn that sets none, on every platform. 32 MiB matches the value CI sets.

Steps to test

1. env -u RUST_MIN_STACK cargo nextest run -p nodedb --test native -E 'test(native_error_code_classification)' → aborts at the default (SIGABRT, rc=100). Re-measured on this branch.
2. RUST_MIN_STACK=33554432 cargo nextest run -p nodedb --test native -E 'test(native_error_code_classification)' → 7 passed.
3. RUST_MIN_STACK=33554432 cargo nextest run -p nodedb --test native -E 'test(vector_search_serializes_distance)' → 1 passed.

Exemption

No red-proof test: this change is documentation only and alters no product behaviour. No issue to close — the stack default is the task.

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[farhan-syah]

Request changes.

Blocker: .cargo/config.toml is not committed in this repository. .gitignore ignores .cargo/ because that file is each contributor's local override ([build] jobs, [patch]). Tracking it makes every existing local copy a merge conflict on the next pull and turns every local edit into a permanent modification. git add -f around the ignore rule is not a fix. Remove the file from the PR.

Where the floor lives instead. CI already sets it: .github/workflows/test.yml exports RUST_MIN_STACK: "33554432" (32 MiB) for the test job, with the reason in the comment above it. The local run must match CI, so the change is one line in CONTRIBUTING.md, in the "Running tests" block next to cargo nextest run --all-features:

RUST_MIN_STACK=33554432 cargo nextest run --all-features

with one sentence on why (debug-profile stack depth, same value CI uses). No config file, no ignore change.

False claim, in the body and in the committed comment. "CI passes at the default because the ci profile has smaller frames" — CI never runs at the default. It runs at 32 MiB (test.yml, RUST_MIN_STACK).

Wrong value. 8 MiB is below the margin the tree documents: nodedb-test-support/src/core_loop_runner.rs states the OS-default 8 MiB blocking-thread stack overflows in debug builds and 32 MiB is sufficient. test.yml chose 32 MiB for that reason. The PR's ladder covers two tests.

Wording. RUST_MIN_STACK is not a floor. It replaces the default size for every std::thread::spawn that sets none, on every platform.

Checked statically against the branch ref. The steps-to-test were not re-run.

[farhan-syah]

False claim. CI does not pass at the default. .github/workflows/test.yml sets RUST_MIN_STACK: "33554432" for the test job. This line is wrong on arrival. Moot once the file goes: see the review body.

[farhan-syah]

Wrong value. nodedb-test-support/src/core_loop_runner.rs documents 8 MiB as insufficient in debug builds and 32 MiB as sufficient. CI runs at 33554432. Local must match CI. Moot once the file goes: the value moves to the CONTRIBUTING.md command line.

[EnRaiha]

Addressed and pushed (8f6369d7c) — the branch now changes CONTRIBUTING.md only.

• Blocker, .cargo/config.toml: removed (94a427886). No config file, no ignore change.
• Where the floor lives: CONTRIBUTING.md, "Running tests" block — one comment sentence plus RUST_MIN_STACK=33554432 cargo nextest run --all-features.
• False claim: body rewritten. It now cites .github/workflows/test.yml:135 (32 MiB) and drops the "ci profile smaller frames" claim.
• Wrong value: 32 MiB (33554432), matching core_loop_runner.rs.
• Wording: body states RUST_MIN_STACK replaces the default stack size for every std::thread::spawn that sets none, on every platform.
• Steps to test, re-run: at the default (env -u RUST_MIN_STACK) the native suite aborts (SIGABRT, rc=100); at 32 MiB native_error_code_classification 7/7 and vector_search_serializes_distance 1/1 pass.

No red-proof test: documentation-only change, stated under "Exemption" in the body.