fix(ci): prevent poisoned Rust caches (#6618)

## Summary

- roll every `Swatinem/rust-cache` use back from v2.9.2 to the last
known-good v2.9.1 digest
- give Unit Tests a new `sherpa-cache-v1` key so it cannot restore the
existing poisoned artifact
- pin Renovate to v2.9.1 and add CI contracts that reject unsafe cache
actions or a misplaced generation key

## Why

After #5441 upgraded rust-cache to v2.9.2, warm-cache `main` Unit Tests
runs began failing while linking `buzz-voice` with `could not find
native static library sherpa-onnx-c-api`. The failed run at `db5617dd1`
restored the same 1.4 KB cache generation that had already failed at
`01091c15a`; the preceding cold run at `26f4c3ed3` downloaded sherpa
1.13.4 and passed.

v2.9.2 changed target cleanup, while `sherpa-onnx-sys` treats its
prebuilt `lib/` directory as proof that the native archive exists.
Rolling back the action and invalidating the affected key removes both
sides of that failure state without disabling target caching.

## Validation

At `6da0037a0407fc498cd482fcbbb74c7a15907e9f`:

- `scripts/test-rust-cache-contract.sh`
- `scripts/test-rust-cache-contract-regressions.sh`
- negative fixtures reject a bad digest in a newly named `.yaml`
workflow and a generation key moved outside the cache action's `with`
block
- YAML parse for all workflows
- release, desktop candidate, mobile release, mobile candidate, and
mobile worktree source contracts
- `just file-size-check`
- pre-commit and pre-push hooks

The PR Unit Tests run proves the cold-cache path because pull requests
restore but do not save Rust caches. The first successful `main` run
after merge will save the new Unit Tests key; the following `main` run
will exercise the warm restore.

## Related issue

None found.

Signed-off-by: Wes <wesbillman@users.noreply.github.com>
Co-authored-by: Carl <32a2e2c9d428ee08902cab75d956da2c1d235a22d4766b0dd4138bf6e2e5db1d@buzz.block.builderlab.xyz>

.github/workflows/ci.yml

@@ -87,6 +87,10 @@ jobs:
           scripts/test-mobile-release-candidate-publisher.sh
       - name: Mobile worktree identity contract
         run: scripts/test-mobile-worktree-overrides.sh
+      - name: Rust cache contract
+        run: |
+          scripts/test-rust-cache-contract.sh
+          scripts/test-rust-cache-contract-regressions.sh
       - name: File size policy
         run: just file-size-check
 
@@ -101,7 +105,7 @@ jobs:
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           save-if: ${{ github.event_name != 'pull_request' }}
       - name: Format check
@@ -123,8 +127,9 @@ jobs:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
       - uses: rui314/setup-mold@9c9c13bf4c3f1adef0cc596abc155580bcb04444 # v1
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
+          key: sherpa-cache-v1
           save-if: ${{ github.event_name != 'pull_request' }}
       - name: Install cargo-nextest
         uses: taiki-e/install-action@0fd46367812ee04360509b4169d9f659d6892bb2 # v2.79.15
@@ -147,7 +152,7 @@ jobs:
           fetch-depth: 2
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
       - uses: rui314/setup-mold@9c9c13bf4c3f1adef0cc596abc155580bcb04444 # v1
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           workspaces: desktop/src-tauri
           save-if: ${{ github.event_name != 'pull_request' }}
@@ -340,7 +345,7 @@ jobs:
           key: relay-artifacts-${{ runner.os }}-${{ hashFiles('crates/**', 'migrations/**', 'Dockerfile', 'Cargo.toml', 'Cargo.lock', 'rust-toolchain.toml', '.cargo/config.toml', '.github/workflows/ci.yml') }}
       - uses: rui314/setup-mold@9c9c13bf4c3f1adef0cc596abc155580bcb04444 # v1
         if: steps.relay-artifacts-cache.outputs.cache-hit != 'true'
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         if: steps.relay-artifacts-cache.outputs.cache-hit != 'true'
         with:
           workspaces: |
@@ -763,7 +768,7 @@ jobs:
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           save-if: ${{ github.event_name != 'pull_request' }}
       # Reuse the relay + git-credential-nostr built by Desktop E2E Relay
@@ -952,7 +957,7 @@ jobs:
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           key: cross-${{ matrix.target }}
           save-if: ${{ github.event_name != 'pull_request' }}
@@ -993,7 +998,7 @@ jobs:
       # toolchain (1.95.0 + clippy via profile = default) comes from the
       # repo-root rust-toolchain.toml, which the runner's preinstalled rustup
       # honors on demand; the host triple already is x86_64-pc-windows-msvc.
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           workspaces: |
             .
@@ -1070,7 +1075,7 @@ jobs:
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           workspaces: desktop/src-tauri
           save-if: ${{ github.event_name != 'pull_request' }}

.github/workflows/mesh-lifecycle.yml

@@ -55,7 +55,7 @@ jobs:
 
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
 
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           save-if: ${{ github.event_name != 'pull_request' }}
 

.github/workflows/release.yml

@@ -511,7 +511,7 @@ jobs:
 
       - uses: cashapp/activate-hermit@cea9af7913204a965fd488637a8d1811bba2e616 # v1
 
-      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+      - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32 # v2.9.1
         with:
           workspaces: desktop/src-tauri
           lookup-only: true