CI paths: Rust Test — add testing-conventions.toml #849

Part of #834. Phase 1 (unanchored corrections — no dependency on any other slice).

What

This is a gap the #834 spec table misses. Row 13 routes testing-conventions.toml to the six Conventions lanes it governs, but rust-test.yml also reads it:

• rust-test.yml:131 runs npx -y testing-conventions unit coverage --language rust packages/rust/src
• that command reads the root testing-conventions.toml by default, taking its floors from [rust.coverage] (lines = 92, functions = 91, regions = 91, branch = 72) and its --features from [rust].features

Python and TS unit coverage moved into the reusable testing-conventions workflow, but Rust's stayed bespoke in rust-test.yml (AGENTS.md: "the Rust core is bespoke in rust-test.yml"). So today, a PR that edits the [rust.coverage] floors does not run the job that enforces them.

Row 13 should read: testing-conventions.toml → the six lanes plus Rust Test. Update the table in #834 when this lands.

Exact change

.github/workflows/rust-test.yml — add one entry to each of the two paths: lists:

on:
  push:
    branches: [main]
    paths:
      - 'packages/rust/**'
      - 'packages/ts/napi/**'
      - 'packages/python/src/**'
      - 'Cargo.toml'
      - 'Cargo.lock'
      - 'testing-conventions.toml'
      - '.github/workflows/rust-test.yml'
  pull_request:
    paths:
      - 'packages/rust/**'
      - 'packages/ts/napi/**'
      - 'packages/python/src/**'
      - 'Cargo.toml'
      - 'Cargo.lock'
      - 'testing-conventions.toml'
      - '.github/workflows/rust-test.yml'

Everything else in this workflow's filter already matches spec rows 3, 5, 7 and 11 exactly — do not change the other entries.

Expected checks on this PR

Files touched: .github/workflows/rust-test.yml only.

MUST run

• Rust Test

MUST NOT run

• Python Test, TS Test, Plugins Test, Python Lint, Python Typecheck, TS Lint, TS Typecheck

May still run (not yet filtered)

• Conventions (all 8 lanes), Release Precheck, Release Config Check, Changelog Check

Optional probe for the new glob: throwaway commit adding a trailing comment line to testing-conventions.toml, confirm Rust Test appears, drop before merging.

Acceptance

• The PR's check list matches the three groups above exactly
• Mergify Merge Protections green
• Row 13 of Epic — CI: run only the checks relevant to the changed paths #834 amended to include Rust Test
• Merge, close this issue

Notes

• No changelog fragment, no e2e attestation. Not anchored in .mergify.yml.