Refactor webview contexts for explicit host ownership

[Henning Dieterichs (hediet)]

Summary

Prepare the webviews for isolated, deterministic rendering without introducing Component Explorer tooling.

• Inject a host that owns persisted state, request/reply messaging, command subscriptions, and one-way notifications.
• Remove pull-request context singletons; production entry points and fixtures explicitly provide their contexts.
• Production entry points use a shared owning provider: preserve the pair across rerenders, dispose context then host on unmount, and allocate a fresh pair on remount. Externally supplied contexts remain caller-owned.
• Rebind Root subscriptions when the supplied context changes.
• Send ready, scroll, debug, and create initialization as notifications without allocating pending reply callbacks.
• Keep ordinary React context consumption, draft persistence, and instance-local timestamp formatting with production defaults.

Review feedback

All eight review comments were valid and are addressed by three focused fixes: owner cleanup, context replacement subscriptions, and one-way notifications. Regression tests cover all three production entry points, repeated mounts, context replacement, pending-request rejection on unmount, and notification retention/error behavior.

Validation

• npm run test:webviews: 85 tests passed, with the normal typed webview build.
• npm run compile:node: extension and webview builds passed.
• npm run lint and npm run hygiene passed.
• Existing quote-reply listener warning remains for Fix webview comment and stack action lifecycle #9049; existing duplicate GraphQL fragment warnings remain in the build.
• No lockfile changes relative to main.

Stack and review scope

• Release completed webview message reply callbacks #9050 (Record-to-Map and completed-reply cleanup) has merged. This PR targets main; those changes are not part of this review diff.
• Fix webview comment and stack action lifecycle #9049 owns the separate comment, avatar-key, and stack-action lifecycle fixes.
• Adopt Component Explorer for webview fixtures #9048 owns Component Explorer adoption, including the viewport-width hook, its call sites, and tests.

Current main was merged while preserving upstream issue previews, mergeability polling, checkout updates, and stack refresh behavior.

[Copilot]

🟡 Changes recommended

Entry points retain host subscriptions after unmount, and context-switching effects remain bound to stale instances.

4 open findings

• Dispose entry-point host and context on unmount · New
• Assert transport listeners are removed after unmount · New
• Clean up host and context on render unmount · New
• Dispose context and host when the tree is unmounted · New

What changed in this PR

Refactors webviews to use explicitly owned hosts and contexts, enabling isolated rendering and deterministic fixtures.

Changes:

• Introduces host-based messaging, persistence, subscriptions, and disposal.
• Adds injectable timestamp formatting and viewport-width behavior.
• Updates production entry points and tests for explicit context ownership.

File	Description
src/​test/​webviews/​testHost.ts	Adds managed test hosts.
webviews/​activityBarView/​app.tsx	Injects an explicit PR context.
webviews/​common/​cache.ts	Removes global state helpers.
webviews/​common/​context.tsx	Makes PR context host-backed.
webviews/​common/​createContextNew.ts	Makes create context host-backed.
webviews/​common/​hooks.ts	Adds injectable viewport width.
webviews/​common/​host.ts	Defines host and transport APIs.
webviews/​common/​message.ts	Refactors request and reply handling.
webviews/​common/​test/​hooks.test.tsx	Tests viewport isolation and cleanup.
webviews/​common/​test/​host.test.ts	Tests host isolation and persistence.
webviews/​components/​sidebar.tsx	Uses the shared viewport hook.
webviews/​components/​test/​timestamp.test.tsx	Tests timestamp formatter isolation.
webviews/​components/​timestamp.tsx	Adds injectable timestamp formatting.
webviews/​createPullRequestViewNew/​app.tsx	Provides an explicit create context.
webviews/​createPullRequestViewNew/​test/​app.test.tsx	Migrates create-view tests to test hosts.
webviews/​editorWebview/​app.tsx	Provides an explicit PR context.
webviews/​editorWebview/​overview.tsx	Uses the shared viewport hook.
webviews/​editorWebview/​test/​app.test.tsx	Migrates root tests to test hosts.
webviews/​editorWebview/​test/​overview.test.tsx	Migrates overview tests to test hosts.
webviews/​editorWebview/​test/​reviewSummary.test.tsx	Migrates review tests to test hosts.

🧠 Review effort: Balanced

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[Copilot]

🟡 Changes recommended

Notification requests and production mounts retain handlers indefinitely, while context subscriptions do not follow provider replacement.

8 open findings

• Resubscribe effect when the context instance changes · New
• Avoid retaining pending replies for notification commands · New
• Resubscribe effect when the context instance changes · New
• Rebind Root subscription when context changes · New
• Dispose context and host when the tree is unmounted
• Clean up host and context on render unmount
• Assert transport listeners are removed after unmount
• Dispose entry-point host and context on unmount

🧠 Review effort: Balanced

[Connor Peet (connor4312)]

Reviewed the complete diff and relevant host, context, entry-point, persistence, and lifecycle code. No actionable P1/P2 security or correctness issues found. No tests or builds were run.

_{Written by Connor's agent running GPT-6.1 Sol}

[Copilot]

🔵 Needs a closer look

Notification commands accumulate unresolved entries in the pending-reply map for the webview’s lifetime.

8 open findings

• Rebind Root subscription when context changes
• Resubscribe effect when the context instance changes
• Avoid retaining pending replies for notification commands
• Resubscribe effect when the context instance changes
• Dispose context and host when the tree is unmounted
• Clean up host and context on render unmount
• Assert transport listeners are removed after unmount
• Dispose entry-point host and context on unmount

🧠 Review effort: Balanced

[Copilot]

🔵 Needs a closer look

Provider replacement retains stale subscriptions, and production-owned hosts remain subscribed after unmount.

8 open findings

• Rebind Root subscription when context changes
• Resubscribe effect when the context instance changes
• Avoid retaining pending replies for notification commands
• Resubscribe effect when the context instance changes
• Dispose context and host when the tree is unmounted
• Clean up host and context on render unmount
• Assert transport listeners are removed after unmount
• Dispose entry-point host and context on unmount

🧠 Review effort: Balanced

The base branch was changed.