Re-land canvas-apps sync reminder hook, fixed for Claude Code

Re-applies the hook from microsoft#320, which was reverted in microsoft#327 because it broke
Claude Code. The hook logic (inject-sync-reminder.cs) is restored byte-for-byte;
only the registration wiring changed.

Two defects in microsoft#320, either one fatal:

1. `"hooks": "hooks/hooks.json"` in .claude-plugin/plugin.json. Claude Code
   rejects the path unless it is `./`-relative, failing installation with
   `Validation errors: hooks: Invalid input`. Even written as
   `"./hooks/hooks.json"` it is redundant — Claude auto-discovers the file, then
   reports the explicit reference as a duplicate hook source and disables the
   plugin's MCP servers. model-apps and power-pages ship working hooks with no
   `hooks` field at all.

2. `userPromptTransformed` in hooks/hooks.json. Claude Code reads that file and
   rejects unrecognized event names, silently discarding the whole file and
   disabling the plugin's canvas-authoring MCP server:
     [ERROR] Failed to load hooks for canvas-apps
     [DEBUG] Plugin not available for MCP - error type: hook-load-failed

Registration now uses the two documented plugin hook formats, so each host reads
only the events it supports:

  Claude Code | hooks/hooks.json (Claude format)      | UserPromptSubmit
  Copilot CLI | hooks.json at plugin root (Copilot)   | userPromptTransformed

Two events are required because the hosts share no usable one: Copilot accepts
UserPromptSubmit as an alias for userPromptSubmitted, but that event has no
output processing, so the reminder would be generated and silently discarded.
Both manifests stay byte-identical mirrors, so the legacy compatibility check is
unaffected.

Also re-applies microsoft#320's removal of the deprecated generate-canvas-app skill,
which the revert restored, and corrects the AGENTS.md claim that Claude Code
"ignores the Copilot-only event and continues loading UserPromptSubmit" — the
behaviour that caused this outage.

Verified on Claude Code 2.1.220 and Copilot CLI 1.0.76-1: plugin installs and
loads (status enabled, MCP intact) and the reminder reaches the model in both
hosts. All four repository validation scripts pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rggammon

plugins/canvas-apps/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "canvas-apps",
-  "version": "2.2.1",
+  "version": "2.2.2",
   "description": "Build Power Apps Canvas Apps using the Canvas Authoring MCP server.",
   "author": {
     "name": "Microsoft",

plugins/canvas-apps/.plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "canvas-apps",
-  "version": "2.2.1",
+  "version": "2.2.2",
   "description": "Build Power Apps Canvas Apps using the Canvas Authoring MCP server.",
   "author": {
     "name": "Microsoft",

plugins/canvas-apps/AGENTS.md

@@ -19,10 +19,15 @@ claude --plugin-dir /path/to/plugins/canvas-apps
 ## Architecture
 
 ```
+.claude-plugin/plugin.json     ← Claude Code metadata (mirrors .plugin/plugin.json)
 .plugin/plugin.json            ← Open Plugins metadata (name, version, keywords)
 .mcp.json                      ← MCP server config (canvas-authoring, auto-registered)
 AGENTS.md                      ← Plugin guidance for AI agents (this file)
 CLAUDE.md                      ← Symlink → AGENTS.md
+hooks.json                     ← Copilot-format hooks: userPromptTransformed
+hooks/
+  hooks.json                   ← Claude-format hooks: UserPromptSubmit
+  inject-sync-reminder.cs      ← File-based .NET app that emits the sync reminder for both hosts
 references/
   TechnicalGuide.md            ← YAML syntax, control selection, layout strategies, Power Fx patterns
   DesignGuide.md               ← Aesthetic guidelines, anti-patterns, design process
@@ -38,8 +43,6 @@ skills/
     SKILL.md                   ← Registers the Canvas Authoring MCP server with Claude Code
   add-data-source/
     SKILL.md                   ← Guides user to add a data source or connector in Studio, then verifies
-  generate-canvas-app/
-    SKILL.md                   ← [DEPRECATED] Redirects to canvas-app
 ```
 
 ## Skills
@@ -75,6 +78,31 @@ The `canvas-authoring` MCP server exposes the following tools:
 | `list_data_sources` | Lists all available data sources in the current authoring session |
 | `sync_canvas` | Syncs the current coauthoring session state from the server to a local directory, writing all YAML files |
 
+## Hooks
+
+Both hosts inject a reminder to call `sync_canvas` before acting, so the agent never edits stale
+local `.pa.yaml` files. The reminder is conditional in wording — the agent skips the sync when no
+coauthoring session is active or the request is unrelated to a canvas app.
+
+Registration uses both plugin [hook formats](https://code.visualstudio.com/docs/agent-customization/agent-plugins)
+— Claude-format (`hooks/hooks.json`) and Copilot-format (`hooks.json` at the plugin root) — which
+the hosts read independently:
+
+| Host | Registered in | Event |
+|------|---------------|-------|
+| Claude Code | `hooks/hooks.json` (Claude format) | `UserPromptSubmit` |
+| Copilot CLI | `hooks.json` in the plugin root (Copilot format) | `userPromptTransformed` |
+
+Each host reads only its own file and ignores the other's. Both run
+`hooks/inject-sync-reminder.cs` via `dotnet run --file`, which branches on its stdin payload to
+emit the output shape each host expects.
+
+Keep the two files separate. Claude Code rejects unrecognized hook event names, so putting
+`userPromptTransformed` in `hooks/hooks.json` makes Claude fail to load the plugin, disabling its
+`canvas-authoring` MCP server. Neither manifest should declare a `"hooks"` field: Claude Code
+auto-discovers `hooks/hooks.json`, and pointing at it explicitly is treated as a duplicate hook
+source, which also disables MCP.
+
 ## Prerequisites
 
 Before the MCP server will start, you need:

plugins/canvas-apps/hooks.json

@@ -0,0 +1,17 @@
+{
+  "version": 1,
+  "description": "Canvas Apps lifecycle hooks (Copilot format)",
+  "hooks": {
+    "userPromptTransformed": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "dotnet run --file \"${PLUGIN_ROOT}/hooks/inject-sync-reminder.cs\"",
+            "timeout": 30
+          }
+        ]
+      }
+    ]
+  }
+}

plugins/canvas-apps/hooks/hooks.json

@@ -0,0 +1,16 @@
+{
+  "description": "Canvas Apps lifecycle hooks",
+  "hooks": {
+    "UserPromptSubmit": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "dotnet run --file \"${CLAUDE_PLUGIN_ROOT}/hooks/inject-sync-reminder.cs\"",
+            "timeout": 30
+          }
+        ]
+      }
+    ]
+  }
+}

plugins/canvas-apps/hooks/inject-sync-reminder.cs

@@ -0,0 +1,63 @@
+#:property PublishAot=false
+
+using System.Text.Json;
+
+// Prompt hook for the canvas-apps plugin.
+//
+// The hook injects guidance instead of calling sync_canvas directly because it only
+// receives the session cwd, not the per-app working directory. A blanket sync could
+// overwrite the wrong directory or clobber local edits that have not been pushed.
+const string Reminder =
+    "Canvas Apps coauthoring reminder: " +
+    "Before acting on this request, if a Canvas Authoring session is " +
+    "active (i.e. `connect` has already been called for a canvas app), first call " +
+    "the `sync_canvas` MCP tool targeting the app's working directory to pull the " +
+    "current session state into the local .pa.yaml files. This avoids editing stale " +
+    "YAML. If no coauthoring session is active yet, or this request is unrelated to " +
+    "a canvas app, skip the sync.";
+
+try
+{
+    var rawInput = await Console.In.ReadToEndAsync();
+    string? transformedPrompt = null;
+
+    try
+    {
+        using var input = JsonDocument.Parse(rawInput);
+        if (input.RootElement.ValueKind == JsonValueKind.Object &&
+            input.RootElement.TryGetProperty("transformedPrompt", out var prompt) &&
+            prompt.ValueKind == JsonValueKind.String)
+        {
+            transformedPrompt = prompt.GetString();
+        }
+    }
+    catch (JsonException)
+    {
+        // Hook failures must not block the user's prompt. If parsing fails, emit the
+        // Claude Code additional-context shape (Copilot will ignore it).
+    }
+
+    using var writer = new Utf8JsonWriter(Console.OpenStandardOutput());
+    writer.WriteStartObject();
+
+    if (transformedPrompt is not null)
+    {
+        writer.WriteString(
+            "modifiedTransformedPrompt",
+            $"{transformedPrompt}\n\n{Reminder}");
+    }
+    else
+    {
+        writer.WriteStartObject("hookSpecificOutput");
+        writer.WriteString("hookEventName", "UserPromptSubmit");
+        writer.WriteString("additionalContext", Reminder);
+        writer.WriteEndObject();
+    }
+
+    writer.WriteEndObject();
+    writer.Flush();
+}
+catch
+{
+    // Hooks are advisory and must never prevent the host from processing a prompt.
+}