Add Java Modernization Studio canvas extension (#2156)

* Add Java Modernization Studio canvas extension

A canvas extension that drives the GitHub Copilot App Modernization for Java workflow from an interactive dashboard: environment readiness checks, repo assessment, prioritized plan/progress, validation gates (CVE scan, test generation), and one-click predefined-task runs — all grounded in the repo's real artifacts (.appmod/assessment.json, plan.md, progress.md). Includes a node:test suite (109 tests) for the grounding logic.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Ayan Gupta <74832088+ayangupt@users.noreply.github.com>

* Secure cockpit loopback server with a per-instance token

Address Copilot review feedback on the Java Modernization Studio canvas:

- Mint a per-instance secret in createInstanceServer, embed it in the
  iframe URL, and validate it on every loopback request (/, /state,
  /events, /action). Other local processes can no longer read repo
  state or dispatch agent actions just by guessing the random port.
  Mirrors the existing diagram-viewer token pattern; the client echoes
  the token from its boot payload. The guard is a no-op when no token is
  set, so direct makeHandler unit tests are unaffected.
- Handle async request-handler rejections in createServer with a .catch
  that returns 500 and logs, instead of leaking an unhandled rejection
  that could destabilize the extension process.
- Tests: token guard 403s unauthenticated /, /state, /events and
  /action and allows valid-token requests; the end-to-end test asserts
  the tokenized URL and a tokenless 403.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix CI: add preview screenshot and clear codespell hits

Add the required assets/preview.png screenshot for the canvas-extension
validator, and resolve two codespell findings in the cockpit:
rename the planSim helper's `nd` variable to `notDone` and reword a
catalog comment to avoid the `invokable`/`invocable` flag.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Harden cockpit loopback server per Copilot review

Address the second-round Copilot review comments on the loopback server:

- broadcast(): drop an SSE client whose write() throws instead of keeping
  it in the Set, so a uncleanly-disconnected client can't cause repeated
  exceptions or leak dead entries on every subsequent broadcast.
- POST /action: treat a malformed JSON body or a missing/invalid "kind"
  as a 400 client error (with an application/json body) instead of a 200
  carrying { ok:false, error:"Unknown action: undefined" }.
- Handler catch: set Content-Type: application/json on the 500 error
  response so it is consistent with the other JSON routes.

Adds four tests covering dead-client eviction, the two 400 paths, and the
JSON-typed 500. Full suite: 115 passing.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Ayan Gupta <74832088+ayangupt@users.noreply.github.com>

* Add canvas.json gallery metadata for Java Modernization Studio

Aaron requested a canvas.json so the awesome-copilot website/gallery can
list this extension. Generated via `npm run website:data`
(writePerExtensionCanvasManifests), which derives id/name/description/
version/keywords/screenshots from package.json + the createCanvas source +
assets, and carries the author through. Output committed verbatim so a CI
regeneration produces no diff.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Ayan Gupta <74832088+ayangupt@users.noreply.github.com>

* Add author tag to package.json

Declare the author in the package manifest (object form, matching the
author already carried in canvas.json so it includes the profile URL).
The published gallery sources author from canvas.json; this adds the
conventional npm author tag to package.json for completeness. Verified
`npm run website:data` still emits the author on the extensions record
and leaves canvas.json byte-identical.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Ayan Gupta <74832088+ayangupt@users.noreply.github.com>

---------

Signed-off-by: Ayan Gupta <74832088+ayangupt@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

extensions/java-modernization-studio/package.json

@@ -0,0 +1,23 @@
+{
+  "name": "java-modernization-studio",
+  "version": "1.0.0",
+  "type": "module",
+  "main": "extension.mjs",
+  "author": {
+    "name": "Ayan Gupta",
+    "url": "https://github.com/ayangupt"
+  },
+  "dependencies": {
+    "@github/copilot-sdk": "1.0.4"
+  },
+  "description": "Drive the GitHub Copilot App Modernization for Java workflow from an interactive canvas: environment readiness, repo assessment, prioritized plan and progress, validation gates, and one-click predefined-task runs grounded in the repo's real artifacts.",
+  "keywords": [
+    "java-modernization",
+    "app-modernization",
+    "azure-migration",
+    "legacy-java",
+    "assessment-dashboard",
+    "validation-gates",
+    "modernization-cockpit"
+  ]
+}