Add create-canvas skill for cloud agent canvas extension authoring by pelikhan · Pull Request #42147 · github/gh-aw

pelikhan · 2026-06-28T23:45:33Z

Summary

Adds a new create-canvas skill for authoring, validating, and debugging canvas extensions in the GitHub Copilot app. Updates AGENTS.md with a routing entry for the new skill.

Changes

`.github/skills/create-canvas/SKILL.md`(new, 259 lines)

New skill covering the full canvas extension lifecycle:

Authoring workflow — 6-step guide: choose scope (project/user/session), scaffold via extensions_manage, edit extension.mjs, reload with extensions_reload, verify with extensions_manage list/inspect, exercise via list_canvas_capabilities / open_canvas / invoke_canvas_action.
Extension shape — entry must be extension.mjs (ES modules; TS not supported); @github/copilot-sdk auto-resolved by CLI; stdout reserved for JSON-RPC; tool names globally unique.
Canvas API — full createCanvas signature: id, displayName, description, inputSchema, actions[] (each requiring handler), open (idempotent), optional onClose. Runtime rules: canvas.* action names reserved; Ajv input schema validation; context field is ctx.canvasId, not ctx.id.
Loopback server pattern — per-instance createServer bound to 127.0.0.1 with OS-assigned port; onClose cleanup; SSE /events for iframe push updates.
ID model — three identifiers: canvasId (type), extensionId (auto-derived ${source}:${name}), instanceId (caller-supplied, max 128 chars, regex-validated).
Agent-side tools — open_canvas, list_canvas_capabilities, invoke_canvas_action.
Injecting instructions — hooks additionalContext path vs systemMessage (append/customize modes); replace mode explicitly prohibited (discards safety guardrails).
State model — key state by document/artifact ID, not instanceId; storage scopes: session workspace, user global, per-artifact, in-repo, per-panel ephemeral.
App theme tokens — CSS custom properties and data-* attributes mirrored by runtime onto the canvas document.
Validation checklist — 5-step RPC sequence: discovery, open, action, input validation, reserved verb rejection.
Debugging guide — extensions_manage inspect surfaces log path and tail; always extensions_reload after edits.
Sharing via Gist — share_extension / install_extension; flat gist format with copilot-extension.json manifest.
Common pitfalls — console.log corrupts JSON-RPC; missing handlers; non-loopback server binding; non-idempotent open; wrong context field; tool name collisions.
Session object quick reference — session.log, session.send, session.sendAndWait, session.on, key event types.

`AGENTS.md`(+1 line)

Added routing entry in the lazy skill loading table for canvas extension tasks pointing to .github/skills/create-canvas/SKILL.md.

File inventory

File	Change	Lines
`.github/skills/create-canvas/SKILL.md`	Added	+259
`AGENTS.md`	Modified	+1

Notes

Documentation and skill files only; no source code changes.
The create-canvas skill is now discoverable via the lazy skill routing mechanism in AGENTS.md.

Generated by PR Description Updater for #42147 · 50.6 AIC · ⌖ 7.36 AIC · ⊞ 4.7K · ◷

Adds .github/skills/create-canvas/SKILL.md with the full canvas/extension authoring reference needed by GitHub Copilot cloud agents. Cloud agents lack the local SDK docs and create-canvas skill context that local sessions receive, so this skill embeds: - Complete authoring workflow (scaffold → edit → reload → verify → drive) - Extension shape and discovery rules - Full canvas API (createCanvas, CanvasOptions, CanvasAction, CanvasError) - Loopback server pattern with lifecycle cleanup - ID model (canvasId vs extensionId vs instanceId) - Agent-side canvas tools (open_canvas, list_canvas_capabilities, invoke_canvas_action) - Instruction injection (additionalContext hooks vs systemMessage) - State model (instanceId vs documentId, storage scopes) - App theme CSS tokens - Validation checklist and debugging steps - Gist sharing format - Common pitfalls Also registers the skill in AGENTS.md lazy-skill routing table. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This PR adds a new lazily-loadable create-canvas skill to provide cloud agents with a self-contained reference for authoring and debugging Copilot app canvas extensions, and wires it into the repository’s skill-routing guidance.

Changes:

Add .github/skills/create-canvas/SKILL.md with canvas extension authoring/debugging guidance, API snippets, and validation steps.
Update AGENTS.md to route canvas/extension work to the new create-canvas skill.

Show a summary per file

File	Description
`AGENTS.md`	Adds a new “use by intent” routing entry for canvas extension work → `create-canvas` skill.
`.github/skills/create-canvas/SKILL.md`	Introduces a comprehensive canvas extension authoring reference for cloud agents (workflow, API, lifecycle, state, theme tokens, validation/debugging).

Review details

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Files reviewed: 2/2 changed files
Comments generated: 6
Review effort level: Low

+2. **Scaffold via tool, don't hand-write the skeleton.**
+ ```
+ extensions_manage({ operation: "scaffold", kind: "canvas", name: "<name>", location: "project" | "user" | "session" })
+ ```
+ The canvas scaffold produces an `extension.mjs` with `joinSession({ canvases: [createCanvas({...})] })`, a working loopback HTTP server per instance, an example action, and `onClose` cleanup. Edit from there.


+
+```
+// Open a canvas panel
+open_canvas({ canvasId: "my-canvas", instanceId: "my-canvas-1", input?: {...} })


+list_canvas_capabilities({ canvasId: "my-canvas" })
+
+// Invoke an action on an open panel
+invoke_canvas_action({ instanceId: "my-canvas-1", actionName: "do_thing", input?: {...} })


+2. **Open** — call `open_canvas({ canvasId, input? })`. Confirm you receive `{ instanceId, url? }` and no error.
+3. **Action** — call `invoke_canvas_action({ instanceId, actionName, input? })` and confirm correct response payload.
+4. **Input validation** — call `open_canvas` with input that fails `inputSchema`. Expect `canvas_input_invalid`.
+5. **Reserved verb rejection** — call `invoke_canvas_action(instanceId, "canvas.open", ...)`. Expect `canvas_reserved_action_name`.


+await session.log("message", { level?: "info"|"warning"|"error", ephemeral?: boolean });
+await session.send({ prompt: "...", attachments?: [{ type: "file", path: "..." }] });


+// session.sessionId — current session ID
+```
+
+Key event types: `assistant.message`, `tool.execution_start`, `tool.execution_complete`, `user.message`, `session.idle`, `session.error`, `permission.requested`, `session.shutdown`.


github-actions · 2026-06-28T23:49:35Z

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Generated by 🧪 Smoke CI for #42147 · ◷

Covers the week's highlights including: - Copilot Canvas extension for agentic workflow operations (PR #42137) - create-canvas skill (PR #42147) - sandbox.agent.sudo: false coverage hits 80% (PR #42119) - Code Scanning Fixer expanded to all severity levels (PR #42139) - mcpg v0.3.32 + firewall v0.27.13 bump (PR #42146) - Agent of the Week: agent-persona-explorer Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-06-29T17:09:17Z

🎉 This pull request is included in a new release.

Release: v0.82.0

CopilotAI review requested due to automatic review settings June 28, 2026 23:45

Copilotstarted reviewing on behalf of pelikhan June 28, 2026 23:46 View session

CopilotAI reviewed Jun 28, 2026
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github-actionsBot mentioned this pull request Jun 28, 2026
[aw] Smoke CI produced no safe outputs #42148
Closed

pelikhan merged commit 59d4d3b into mainJun 28, 2026
21 checks passed

pelikhan deleted the pelikhan-canvas-extension-skill branch June 28, 2026 23:50

This was referenced Jun 29, 2026
[blog] Weekly blog post – 2026-06-29 #42167
Merged
[code-simplifier] simplify: merge parallel status switch statements into lookup table in dashboard app.ts #42171
Closed

CopilotAI mentioned this pull request Jun 29, 2026
[code-simplifier] Consolidate dashboard status label mapping and align pagination slice style #42180
Merged

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Add create-canvas skill for cloud agent canvas extension authoring - #42147

Add create-canvas skill for cloud agent canvas extension authoring#42147
pelikhan merged 1 commit into
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		await session.log("message", { level?: "info"\|"warning"\|"error", ephemeral?: boolean });
		await session.send({ prompt: "...", attachments?: [{ type: "file", path: "..." }] });

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Summary

Changes

.github/skills/create-canvas/SKILL.md(new, 259 lines)

AGENTS.md(+1 line)

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pelikhan commented Jun 28, 2026•
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`.github/skills/create-canvas/SKILL.md`(new, 259 lines)

`AGENTS.md`(+1 line)