Add Devin plugin (plugins/devin): MCP server + ATIF-v1.7 harvest

Wires the skillopt_sleep engine into Devin (Cognition) via an MCP server,
following the same thin-shell pattern as plugins/copilot.

- mcp_server.py: stdlib-only stdio MCP server exposing the standard sleep_*
  tools (status, dry-run, run, adopt, harvest). REPO_ROOT defaults to ../.. so
  it finds skillopt_sleep automatically when run from plugins/devin/.
- harvest_devin.py: converts Devin ATIF-v1.7 transcripts, agentmemory, and
  .devin/skills/*/SKILL.md into the Claude Code-compatible JSONL the engine
  consumes; enriches with taskKey + outcome envelopes (hard test/build signal
  or judge rubric). Workspace auto-detection; cross-platform paths.
- judge.py, mcp-config.example.json, devin-rules.snippet.md, README.md.
- plugins/README.md: add Devin to the platform + install tables.

No changes to skillopt_sleep; shells out to `python -m skillopt_sleep` like the
other plugins. Pure stdlib; default backend mock (no API spend).

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

plugins/devin/README.md

@@ -0,0 +1,63 @@
+# SkillOpt-Sleep — Devin integration
+
+Give **Devin** (Cognition) a nightly **sleep cycle** via a tiny **MCP server**
+that exposes the `skillopt_sleep` engine as tools. MCP is Devin's supported way
+to add custom tooling, so this works in Devin's CLI and IDE.
+
+Devin doesn't write transcripts in the format the engine consumes, so this
+plugin adds a **Devin-specific harvester** that converts every locally available
+source into the Claude Code-compatible JSONL the engine reads.
+
+## What's here
+
+| File | Purpose |
+|---|---|
+| `mcp_server.py` | stdlib-only MCP (stdio) server exposing `sleep_*` tools |
+| `harvest_devin.py` | converts Devin ATIF-v1.7 transcripts + agentmemory + `.devin/skills` into JSONL, with `taskKey` + outcome envelopes |
+| `judge.py` | reference judge for the deferred/judge branch of the validation gate |
+| `mcp-config.example.json` | drop-in MCP server config |
+| `devin-rules.snippet.md` | paste into `.devin/rules/skillopt-sleep.md` |
+
+## What it harvests
+
+| Source | Where |
+|---|---|
+| Devin transcripts (ATIF-v1.7) | `~/.local/share/devin/cli/transcripts/*.json` |
+| agentmemory | `~/.agentmemory/standalone.json` |
+| Skill files | `.devin/skills/*/SKILL.md` |
+
+Workspaces are auto-detected from `~/.config/Devin/User/workspaceStorage/*/workspace.json`.
+After `sleep_adopt`, the evolved skill is synced to `.devin/skills/skillopt-sleep-learned/SKILL.md`.
+
+## Install
+
+Requires Python ≥ 3.10. No third-party packages — the server is pure stdlib.
+
+1. **Register the MCP server.** Use `mcp-config.example.json` as a template; set
+   `args` to the absolute path of this `mcp_server.py`. The engine is found
+   automatically (this plugin lives inside the SkillOpt repo). Or via the Devin
+   CLI:
+
+   ```bash
+   devin mcp add skillopt-sleep \
+     --env "SKILLOPT_DEVIN_CLAUDE_HOME=$HOME/.skillopt-sleep-devin" \
+     -- python3 /abs/path/to/SkillOpt/plugins/devin/mcp_server.py
+   ```
+
+2. **(Optional)** copy `devin-rules.snippet.md` to `.devin/rules/skillopt-sleep.md`
+   so Devin proactively offers the tools.
+
+3. Ask Devin: *"run the sleep cycle"*, *"what did the last sleep propose?"*, *"adopt it"*.
+
+## Tools
+
+| Tool | What it does |
+|---|---|
+| `sleep_status` | nights run so far + latest staged proposal |
+| `sleep_dry_run` | preview cycle — no staging, no changes |
+| `sleep_run` | full cycle; stages a proposal for review |
+| `sleep_adopt` | apply the staged proposal; syncs skill to the workspace |
+| `sleep_harvest` | debug: list the recurring tasks mined |
+
+Default backend is `mock` (no API spend); `--backend claude|codex` uses your own
+budget. Same engine as the other plugins — all call `python -m skillopt_sleep`.