fix(text): close Milestones 6 and 8 lifecycle gaps

[thejustinwalsh]

Summary

• keep pnpm as the repository's single workflow surface while mise supplies only the exact pinned Node, pnpm, Rust, and workload-scoped native tools
• scope optional Meson, Ninja, and pipx provisioning to the benchmark app and document the HarfBuzz prerequisites without forcing them onto core contributors
• close the remaining Text generation-lifecycle gaps around pending no-ops, callback ownership, failed retries, paint identity, font invalidation, and explicit disposal
• remove stale benchmark React surfaces and retain React Doctor's explicit non-route entrypoint coverage
• complete the deferred combined Milestone 6/8 adversarial review, independently remediate every actionable finding, and close both milestones in the canonical roadmap

Lifecycle guarantees

• a pending semantic no-op cannot cancel or strand the generation that owns it
• callback-only and rejected generations retain deterministic ownership and retry behavior
• paint-only mutation preserves the generation identity used by font-disposal listeners
• disposing a superseded font cannot invalidate a healthy replacement generation
• explicit Text.dispose() clears terminal invalidation state

Toolchain boundary

Mise selects pinned tools; it does not define a parallel task graph. Humans with compatible tools may run the named pnpm scripts directly. Repository agents and CI enter the pinned environment with mise exec -- pnpm … and execute those same scripts. Optional HarfBuzz build tools live under apps/benchmarks/mise.toml, outside the core Rust-and-Node contribution path.

Verification

• complete root pnpm check
• Text integration: 182 passed
• benchmark unit: 257 passed; benchmark script tests: 4 passed
• complete Chromium headless conformance and packed-consumer execution
• Japanese showcase subset freshness check
• package-size and fail-closed autoresearch provenance checks
• OKF validation: 0 conformance errors, 0 producer-profile errors, 0 warnings
• independent Claude closure review: no unresolved actionable Milestone 6/8 finding

The browser core delta for the lifecycle fixes is +678 raw / +391 minified / +75 gzip / +106 Brotli bytes. Optional baker hosts and Wasm artifacts remain byte-identical, and all compressed absolute budgets remain unchanged.

Stack

Depends on #10 and completes the Milestone 8.6 stack. No experimental raster kernel ships from this layer.