Adding support for Copilot Marketplace plugin (#47)

* Add GitHub Copilot plugin and marketplace manifests for Ponytail

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

* Add Copilot hook adapters and plugin data runtime precedence

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

* Document Copilot plugin install flow and instruction fallback mode

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

* Fix Copilot hooks for native output context and state-only mode tracking

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

* docs: add Copilot CLI namespaced command examples

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

* Collapse Copilot hooks into shared activate/mode-tracker

The Copilot hook files duplicated ponytail-activate.js and
ponytail-mode-tracker.js, differing only in output shape. Move that
difference into writeHookOutput (isCopilot branch) and point
copilot-hooks.json at the shared hooks. Deletes both forks (-73 lines).

Refs #1

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* Align Copilot manifest version to 4.4.0 with cross-manifest parity test

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

* Make Copilot and Codex host detection exclusive in runtime output routing

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

* Add Copilot debt command validation with a pull request acceptance checklist

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

* Removed PR template

* Drop tautological copilot command-form test

The namespaced-form assertion built '/ponytail:ponytail-debt' from two
constants and compared it to itself — it tests string concatenation, not
wiring. The file-exists check above already catches a renamed manifest.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

hooks/copilot-hooks.json

@@ -0,0 +1,21 @@
+{
+  "version": 1,
+  "hooks": {
+    "sessionStart": [
+      {
+        "type": "command",
+        "bash": "node \"${PLUGIN_ROOT}/hooks/ponytail-activate.js\"",
+        "powershell": "node \"${PLUGIN_ROOT}\\hooks\\ponytail-activate.js\"",
+        "timeoutSec": 5
+      }
+    ],
+    "userPromptSubmitted": [
+      {
+        "type": "command",
+        "bash": "node \"${PLUGIN_ROOT}/hooks/ponytail-mode-tracker.js\"",
+        "powershell": "node \"${PLUGIN_ROOT}\\hooks\\ponytail-mode-tracker.js\"",
+        "timeoutSec": 5
+      }
+    ]
+  }
+}

hooks/ponytail-runtime.js

@@ -2,10 +2,15 @@ const fs = require('fs');
 const path = require('path');
 const { getClaudeDir } = require('./ponytail-config');
 
-const isCodex = Boolean(process.env.PLUGIN_DATA);
-const statePath = isCodex
-  ? path.join(process.env.PLUGIN_DATA, '.ponytail-active')
-  : path.join(getClaudeDir(), '.ponytail-active');
+const STATE_FILE = '.ponytail-active';
+const isCopilot = Boolean(process.env.COPILOT_PLUGIN_DATA);
+const isCodex = !isCopilot && Boolean(process.env.PLUGIN_DATA);
+
+let stateDir = getClaudeDir();
+if (isCodex) stateDir = process.env.PLUGIN_DATA;
+if (isCopilot) stateDir = process.env.COPILOT_PLUGIN_DATA;
+
+const statePath = path.join(stateDir, STATE_FILE);
 
 function setMode(mode) {
   fs.mkdirSync(path.dirname(statePath), { recursive: true });
@@ -17,23 +22,30 @@ function clearMode() {
 }
 
 function writeHookOutput(event, mode, context = '') {
-  if (!isCodex) {
-    process.stdout.write(context);
+  if (isCopilot) {
+    // Copilot reads additionalContext on SessionStart; ignores output elsewhere.
+    process.stdout.write(JSON.stringify(
+      event === 'SessionStart' && context ? { additionalContext: context } : {}));
     return;
   }
-  const output = { systemMessage: `PONYTAIL:${mode.toUpperCase()}` };
-  if (context) {
-    output.hookSpecificOutput = {
-      hookEventName: event,
-      additionalContext: context,
-    };
+  if (isCodex) {
+    const output = { systemMessage: `PONYTAIL:${mode.toUpperCase()}` };
+    if (context) {
+      output.hookSpecificOutput = {
+        hookEventName: event,
+        additionalContext: context,
+      };
+    }
+    process.stdout.write(JSON.stringify(output));
+    return;
   }
-  process.stdout.write(JSON.stringify(output));
+  process.stdout.write(context);
 }
 
 module.exports = {
   clearMode,
   isCodex,
+  isCopilot,
   setMode,
   writeHookOutput,
 };