feat(mcp): serve per-page resource templates and list_changed - #417

What and why

The "per-page resource templates and list_changed" item from #372.

The six page-scoped agent resources mix every connected page together, so an agent with several tabs open can't read one tab's data as a resource. The HTTP MCP endpoint now serves a resource template per page resource:

pangular://page/{pageId}/component-tree
pangular://page/{pageId}/signal-graph
pangular://page/{pageId}/injector-tree
pangular://page/{pageId}/ngrx-store
pangular://page/{pageId}/forms
pangular://page/{pageId}/router

• Each read filters the live shared state to that page and reuses the existing resource formatters, so masking is unchanged. Reads renew the agent lease first, like the existing resources. Panel selection fields (selectedId and the like) are left out.
• An unknown pageId answers in markdown with the pages that do report that data.
• resources/list also names the concrete per-page entries, for clients that don't read templates.
• A template is offered only while its resource is (agentResourceOffered: inspector on and agent.tools on). The static resources are unchanged.
• notifications/resources/list_changed fires when a page connects or is forgotten: the server watches the shared states' updated events, waits 500 ms, and notifies only when the set of page ids changed. No timer runs while idle.
• Templates are route options, not ctx.agent registrations, so they have no AGENT_ENTRIES entries. A new test asserts the template names match the page resource entries exactly.

devframe patches

devframe 1.2.5 has no resource templates, and the host can't fire list_changed itself. Like prompts in #416, the local patches gain two route options, threaded through resolveMcpConfig, mountMcpRoute, hub initiate, createMcpFetchHandler and stdio createMcpServer:

• resourceTemplates: resources/templates/list answers; resources/read tries the templates (level-1 {var}, one percent-decoded segment, no /) before the "unknown resource URI" error; resources/list adds each template's list() entries.
• onResourcesChanged(notify): bridgeListChanged feeds it into the resources sink, on HTTP and stdio.
• Without them the server behaves exactly as before. pnpm-lock.yaml only changes the three patch hashes.

Left out

• stdio offers no templates: it doesn't go through pangularMcp(), and no page connects there.
• No resources/subscribe / notifications/resources/updated; only the list notification.
• An installed package has neither option until devframe ships them upstream. The docs say so.

Docs: templates and list_changed in agents/mcp-server.md, a "Read one page" section in agents/resources.md, the patched-dependencies row in the contributing guide, and the Resource entry in docs/CONTEXT.md.

Refs #372.

How it was verified

• pnpm install --frozen-lockfile (the patches apply)
• pnpm commit:check
• pnpm format:check
• pnpm typecheck
• pnpm test:devtools (3201). New agent-page-resources.test.ts (16 tests) and one in agent-metadata.test.ts: template gating; per-page filtering of each state; the debounced notifier with fake timers; through the real hub endpoint, templates/list, different data for two pages, the unknown-page answer, no match for an extra / segment, concrete entries in resources/list, an inspector turned off, resourceTemplates: []; on a real subscriptions/listen stream, list_changed when a page connects and when it is forgotten, and not for a repeat push; the dev route.
• pnpm skills:check
• Docs in apps/docs updated and pnpm docs:build passes
• pnpm extension:build: no change to extension/ui

Summary by CodeRabbit

• New Features
  • MCP clients can now access page-specific component trees, signal graphs, injector trees, NgRx state, forms, and router state through resource templates.
  • Resource listings update when pages begin or stop reporting. Requests for pages without available data receive a descriptive response.
• Documentation
  • Added guidance on page-specific resources, resource templates, and their availability across MCP endpoints.