feat: add Linear issue delivery, plugin reliability, and four-stage SDLC

[IchenDEV]

Outcome

Linear issues can now start a durable CodeTwo task and worktree, produce commit-bound validation evidence, create an authorized PR, continue from review feedback, and synchronize actual merge results. Credentials stay in the system keyring; interrupted work and tracker synchronization recover independently.

The plugin runtime now bounds messages, concurrency, and command duration, and the desktop consumes one atomic plugin snapshot. New SDLC changes use Intent, Spec, Plan, and Verification files while reusing ordinary implementation authorization and requiring additional high-risk design confirmation.

Change record

• Change: docs/sdlc/changes/2026-09-08-plugin-runtime-reliability/change.md
• Change: docs/sdlc/changes/2026-09-08-linear-issue-delivery/change.md
• Change: docs/sdlc/changes/2026-09-08-four-stage-sdlc/intent.md
• Change: docs/sdlc/changes/2026-09-03-ultracite-init/intent.md
• Change: docs/sdlc/changes/2026-09-06-desktop-ci-speed/intent.md

Validation

• Linear adapter: 14 tests; desktop host: 42 tests; plugin crate: 145 unit/integration tests.
• Desktop: 876 tests; strict Ultracite checks, TypeScript, and production renderer build.
• Lifecycle: 28 tests and 217 assertions, including CI-pinned Bun 1.3.10; documentation and branch-scope gates.
• Independent review covered the adapter, host recovery, four-stage contract, and frontend merge. Browser checks covered the real dialog with fixture API data in light and dark views.
• Two upstream historical records had duplicate AC mappings; supporting evidence was retained without changing their decisions or results.
• Integrating current main exposed a missing React-18 compiler runtime dependency; declaring the matching runtime restored the production build.

Live Linear/GitHub account writes, system-keyring round trips, signed desktop packaging, and cross-platform runtime acceptance remain unverified. Attachment support currently provides metadata and links. Existing renderer chunk-size warnings remain; workspace-wide Rust formatting has pre-existing differences outside this change.

Review and release

• Acceptance evidence covers the current diff, including rendered UI where affected.
• Required checks passed; failures and skipped checks are explained in the records.
• Merge authorization: not requested.
• Release authorization: not requested.