refactor(desktop): key transcript diagram lifetimes

[tonyfettes]

Summary

• project transcript content into channel/session-scoped keyed Rabbita blocks so unchanged historical Markdown is not reparsed on streaming updates
• have Markdown report exact generated diagram wrappers and give each wrapper its own after-render viewport subscription
• add a public exact-wrapper DiagramViewport lifetime while keeping the existing multi-diagram API for Editor hosts
• leave the transcript root observer responsible only for mount, geometry, and local-image DOM signals

Stack

• base: refactor(viewer): share diagram viewport controls #857 (codex/shared-diagram-viewports)
• rebase this PR onto main after refactor(viewer): share diagram viewport controls #857 merges

Validation

• moon check --target native --deny-warn
• moon check --target js --deny-warn
• moon fmt --check
• moon test --target native (3447 passed)
• moon test --target js (2905 passed)
• moon cram test tests/cram (27 passed)
• moon test --target all (editor: 1372 wasm + 295 wasm-gc passed)
• Playwright smoke + component suites (143 passed)
• moon build --target native
• moon build --target js

just is unavailable in this checkout environment, so the repository recipes were expanded and run directly.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Remount diagram lifetimes with the Chat DOM

When view replaces the Chat subtree with Skills, Settings, or the signed-out gate, the transcript component and these assoc_by subscriptions remain alive, so this one-shot lookup either keeps a controller attached to the removed wrapper or returns while no wrapper exists. Returning to Chat creates a new transcript DOM without reloading the unchanged subscription, leaving existing UML diagrams without interactive controls and retaining listeners for the detached wrapper. Tie the diagram lifetime to the transcript DOM mount generation or retry/dispose it from the root mount observer.

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