fix(e2e): explicit Cargo feature + stage fixtures into Tauri $TEMP scope

[shyhunter]

Summary

Two adjacent fixes that together unblock npm run test:e2e on macOS, addressing the long-standing E2E breakage flagged in yesterday's security-hardening session.

1. Cargo debug_assertions predicate → explicit e2e feature

The previous [target.'cfg(debug_assertions)'.dependencies] form was incorrect: Cargo evaluates [target.<cfg>.dependencies] against target spec triples and target features, not against rustc's debug_assertions flag. This produced an unexpected-cfg warning and made plugin inclusion non-deterministic.

Replaced with an opt-in e2e Cargo feature. tauri-plugin-webdriver-automation now compiles in only when built with --features e2e; release builds are unaffected.

2. Stage e2e fixtures into Tauri's $TEMP capability scope

Tauri's fs capability scope (src-tauri/capabilities/default.json) only permits reads from $DOCUMENT / $DOWNLOAD / $DESKTOP / $TEMP. Real fixtures live in ~/papercut/test-fixtures/, which is outside every allowed scope. Every PDF/Image E2E test was failing with Timed out waiting for step 1 because:

handleFileSelected(path)
  → getFileSizeBytes(path)        ← Tauri fs scope check fails
  → catch sets corruptFileError   ← step never advances

src/e2e/helpers/driver.ts already documented the intended fix ("CI can place [fixtures] inside /tmp (within Tauri's $TEMP fs scope)"), but the staging wiring was missing.

Now: at the top of wdio.conf.ts we copy real fixtures into ${os.tmpdir()}/papercut-e2e/real/, and generate-e2e-fixtures.mjs writes generated error-path fixtures (large-sparse.*, corrupt.*) into ${os.tmpdir()}/papercut-e2e/error/. The driver helper picks both up via E2E_*_DIR env vars set by the same code (CI overrides still win via ??=).

Result

• Before: 100% of PDF tests failed at Timed out waiting for step 1.
• After: Success-case PDF compression tests (PDF-Q-WEB / SCREEN / PRINT) all pass in ~21s.
• A separate upstream issue (lock poisoned: PoisonError in tauri-plugin-webdriver-automation 0.1.3 across test transitions) blocks the remaining tests. Tracked upstream — out of scope for this PR.

New build command

npm run e2e:build
# alias for: tauri build --debug --features e2e --bundles app

The previous command (npm run tauri -- build --debug --bundles app) no longer compiles the plugin in. The --bundles app flag is still required because the default DMG bundling step deletes the .app that wdio expects.

Files changed

• src-tauri/Cargo.toml — [features] + optional = true dep
• src-tauri/src/lib.rs — #[cfg(feature = "e2e")]
• src/e2e/wdio.conf.ts — top-of-file fixture staging
• src/e2e/fixtures/generate-e2e-fixtures.mjs — write to $TMPDIR/papercut-e2e/error/
• package.json — new e2e:build script

Security notes (R015)

• No secrets touched. No Tauri capability scope expanded — fix uses only the existing $TEMP allowlist already in default.json.
• The e2e Cargo feature is opt-in; never set in any production/release build path. Renderer→Rust trust boundary (P014) unchanged.
• Risk to flag: if a future CI/release workflow accidentally adds --features e2e to a packaged build, it would expose the WebDriver automation port (4444) to whoever runs the resulting .app. Suggest a follow-up note in .claude/project_rules_decisions.md under P013 reinforcing that e2e must remain off in any release-path build.

Test plan

• cargo check --manifest-path src-tauri/Cargo.toml — clean (no e2e feature)
• cargo check --manifest-path src-tauri/Cargo.toml --features e2e — clean (with e2e feature)
• npm run test — 503/503 passing
• npx tsc --noEmit (main) — clean
• npm run e2e:build then npm run test:e2e:pdf — PDF-Q-WEB/SCREEN/PRINT pass; further tests blocked by the upstream PoisonError noted above
• npm audit --omit=dev — 0 advisories (per P015)

🤖 Generated with Claude Code

[shyhunter]

Upstream issue filed: danielraffel/tauri-webdriver#4