Summary

• expose Prompt Shaper and other composer plugins in pre-child, existing-child, and queued-message side-chat composers
• add the minimal public side-chat composer scope contract and generated SDK/template declarations
• retain side-chat drafts while isolating inactive/unmounted plugin accessories and stale async ownership

Validation

• review-loop: CORRECT from all final reviewers
• focused app: 7 files, 171 tests
• focused plugin SDK: 2 files, 17 tests
• full plugin SDK/templates: 12 files, 72 tests
• full app: 249 files, 1,749 tests
• app/plugin SDK/templates typecheck, app lint, app/plugin SDK build, declaration/template generation checks, and git diff --check
• desktop QA with Prompt Shaper 3529edd896569f156698ea582ce426117dd65144: pre-child/existing child, parent-draft and attachment isolation, completion, Undo, cancellation/late-result cleanup, and queued side-chat editing

Stacked on ymichael#809 (bb/prompt-shaper-composer-shimmer) at 91866739cf31a0d414750eb627d9c810d480024a.