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

[erkamyaman]

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.

[coderabbitai]

📝 Walkthrough

The change adds MCP resource templates for six page-scoped devtools resources. Clients can list and read resources for reporting pages. The MCP route forwards resource templates and page-change notifications, and tests and documentation describe the new behavior.

Changes: Page-scoped MCP resources

Layer / File(s)	Summary
MCP resource-template transport patches/devframe@1.2.5.patch, patches/@devframes__hub@1.2.5.patch, patches/@devframes__agentic@1.2.5.patch	The patches add resource-template and resource-change options to MCP route types and forward them to the server. The server lists templates, matches and reads resource URIs, and forwards change notifications. The agentic patch also adds prompt handlers and direct returns for valid mcpContent tool results.
Page resource data and change tracking packages/devtools/src/agent-page-resources.ts, packages/devtools/src/config.ts	The new source formats six resource types for individual pages, lists reporting page IDs, and debounces page-set notifications by 500 ms. Resource availability follows agent and inspector configuration.
Devtools resource registration packages/devtools/src/agent-mcp.ts, packages/devtools/src/devframe.ts	The devframe registers templates for the six resources. pangularMcp supplies default templates and a page-change hook when the caller has not provided them.
Behavior verification and documentation packages/devtools/src/__tests__/*, apps/docs/src/content/agents/*, apps/docs/src/content/contributing/development.md, docs/CONTEXT.md	Tests cover metadata, page-filtered reads, configuration, notifications, and route behavior. Documentation describes template reads and listings, notification behavior, and patch availability.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant MCPClient
  participant MCPServer
  participant PageResourceTemplate
  participant PageResourceSource
  participant SharedStates
  MCPClient->>MCPServer: List resource templates
  MCPServer-->>MCPClient: Return configured templates
  MCPClient->>MCPServer: Read page resource URI
  MCPServer->>PageResourceTemplate: Match URI and call read
  PageResourceTemplate->>PageResourceSource: Read resource for pageId
  PageResourceSource->>SharedStates: Read current resource state
  SharedStates-->>PageResourceSource: Return resource state
  PageResourceSource-->>MCPClient: Return page-scoped resource text

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Merge Risk: 🔵 Low · up to 3b294

The resource documentation has a small visible typo, but the identified notification-order concern does not block page-change notifications. The change is mergeable with a documentation fix.

Security architecture risk: 🔵 Low · up to 3b294

The new resources select data already available through existing resources and retain the existing access controls. No introduced security concern was established, but complete connection and shutdown behavior has not been verified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The relevant data exposure remains the enabled resource data of pages held by one agent host. Page IDs select data within that host; they are not a new tenant-authorization boundary. Existing aggregate resources already exposed the corresponding page states to authorized resource readers.

Trust Boundaries and Controls

• observed — The caller-controlled resource URI reaches a configured template matcher and then a page-filtered read from the current host's source. The inspected route changes preserve identity and origin option forwarding; they do not add a separate transport or privileged execution sink.

Resilience and Maintainability Implications

• observed — Abrupt transport closure marks page ownership disconnected but does not immediately remove every retained report. New listings follow retained shared-state membership rather than connection liveness. This retention and periodic expiry predate the PR, and the same data was available through aggregate resources; it is not retained as an introduced security concern.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 78.95% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 6 files. (7 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main changes: per-page MCP resource templates and resources/list_changed notifications.

Full details: Docstring Coverage

Explanation

Docstring coverage is 78.95% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 6 files. (7 skipped: 7 unsupported.)

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☁️ Nx Cloud last updated this comment at 2026-10-15 22:23:51 UTC

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @apps/docs/src/content/agents/resources.md:
- Line 87: Remove the stray asterisk before “MCP resource template” in the
sentence describing the HTTP endpoint and `resources/templates/list`, leaving
the surrounding wording unchanged.

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📥 Commits

Reviewing files that changed from the base of the PR and between e0d0ebe and 3b294c6.

⛔ Files ignored due to path filters: 1

• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing: 13

• apps/docs/src/content/agents/mcp-server.md
• apps/docs/src/content/agents/resources.md
• apps/docs/src/content/contributing/development.md
• docs/CONTEXT.md
• packages/devtools/src/__tests__/agent-metadata.test.ts
• packages/devtools/src/__tests__/agent-page-resources.test.ts
• packages/devtools/src/agent-mcp.ts
• packages/devtools/src/agent-page-resources.ts
• packages/devtools/src/config.ts
• packages/devtools/src/devframe.ts
• patches/@devframes__agentic@1.2.5.patch
• patches/@devframes__hub@1.2.5.patch
• patches/devframe@1.2.5.patch

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