refactor(plugin): collapse three host bundles into one shared plugin/ tree

Merge the byte-duplicated claude-plugin/, codex-plugin/, and cursor-plugin/
trees into a single shared plugin/ tree with per-host manifest overlays,
and route all three installers through a new composed embed registry
(src/agents/plugin_bundle.rs). Each host still deploys a byte-for-byte
identical tree to before — verified by installing every host from the new
layout and diffing sha256 hashes against the pre-refactor deploy.

Layout (plugin/):
- skills/                 17 shared model-invocable skills + 13 canonical
                          (claude/codex form) tracedecay-* workflow dispatchers
- overlays/cursor/skills/ 13 Cursor dispatcher slugs (disable-model-invocation
                          form) — deployed by Cursor in place of the canonical
                          dispatchers at the same skills/ deploy path
- overlays/cursor/agents/ Cursor-form subagents
- agents/                 Claude-form subagents
- commands/               13 Claude slash commands
- rules/                  2 Cursor .mdc rules
- hooks/hooks-<host>.json per-host hook wiring (each deploys as hooks/hooks.json)
- .{claude,cursor,codex}-plugin/  host manifests (unchanged deploy contents)
- .mcp.json               shared Claude/Codex MCP config (byte-identical)
- mcp-cursor.json         Cursor MCP config (deploys as mcp.json)
- README-<host>.md        per-host README (deploys as README.md)

src/agents/plugin_bundle.rs owns CANONICAL_PLUGIN_FILES plus the per-host
manifest slices and composes each installer's deploy set as
CANONICAL ∪ <HOST>_MANIFEST. Each PluginFile.relative is the deploy path
(unchanged from the legacy bundles); contents are include_str!'d from the
shared plugin/ source, whose path may differ (e.g. Cursor's hooks/hooks.json
is sourced from plugin/hooks/hooks-cursor.json).

cursor.rs/codex.rs/claude.rs drop their per-host EMBEDDED_PLUGIN_FILES tables
and consume plugin_bundle::{cursor,codex,claude}_files(); deploy/render/
migrate/doctor logic is unchanged. steering.rs bootstrap include repoints to
plugin/skills/using-tracedecay/SKILL.md.

Track plugin/.mcp.json past .gitignore; add /plugin/** to the Cargo publish
include list (replacing the cursor/codex bundle globs).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ScriptedAlchemy

.github/workflows/plugin-validation.yml

@@ -12,8 +12,7 @@ name: Plugin Validation
 on:
   pull_request:
     paths:
-      - "cursor-plugin/**"
-      - "codex-plugin/**"
+      - "plugin/**"
       - "tests/fixtures/cursor-schemas/**"
       # Plugin/skill test modules (e.g. plugin_manifest_schema_test.rs,
       # plugin_skill_contract_test.rs, the skill lint tests).
@@ -65,15 +64,15 @@ jobs:
         run: |
           npx --no-install ajv validate --spec=draft7 -c ajv-formats --errors=text \
             -s tests/fixtures/cursor-schemas/plugin.schema.json \
-            -d cursor-plugin/.cursor-plugin/plugin.json
+            -d plugin/.cursor-plugin/plugin.json
 
       # The Codex manifest follows Codex's own layout (e.g. its `interface`
       # block), so the Cursor schema does not apply; keep it to a strict JSON
       # well-formedness check alongside the other bundle JSON files.
       - name: Check bundle JSON files parse
         run: |
           set -euo pipefail
-          find cursor-plugin codex-plugin -name '*.json' -print0 |
+          find plugin -name '*.json' -print0 |
             while IFS= read -r -d '' f; do
               python3 -c "import json,sys; json.load(open(sys.argv[1]))" "$f" \
                 || { echo "invalid JSON: $f" >&2; exit 1; }

.gitignore

@@ -3,8 +3,7 @@
 .codegraph
 .tracedecay
 .mcp.json
-!codex-plugin/.mcp.json
-!claude-plugin/.mcp.json
+!plugin/.mcp.json
 .claude/
 .cursor/
 docs/superpowers

Cargo.toml

@@ -25,8 +25,7 @@ include = [
     "/benches/**",
     "/examples/**",
     "/benchmarks/queries/default.toml",
-    "/cursor-plugin/**",
-    "/codex-plugin/**",
+    "/plugin/**",
     "/vendor/**",
     "/dashboard/shell/dist/**",
     "/dashboard/holographic/dist/**",