refactor(prime-agent): extract the /mcpctl switcher to typechecked source; pi --dry-run; docs

The prime-agent switcher existed only as a 275-line string literal inside
prime-agent-extension.ts, so nothing typechecked or linted it — the exact gap
that let a wrong ctx.ui.select() option shape ship in the pi extension. It now
lives at src/prime-agent-ext/mcpctl-switch.ts with a generator, a tsconfig
checking it against the real @earendil-works/pi-coding-agent types, eslint
coverage and an embed-freshness test, matching pi and opencode.

The extraction was verified byte-identical before any edit, so the behaviour
shipped today is exactly what was captured. Linting it then found six problems
in code nothing had ever checked: object-truthiness null guards, a nullable
string conditional and a missing return type. All behaviour-preserving to fix,
but exactly the class of thing that ships silently when nothing is looking.

Also:

  - `config pi` gains --dry-run, the last agent without it.
  - The SessionStart hook installer now drops untagged duplicates of its own
    exact command — rows left behind before the marker existed, or by a suite
    that used to write into a real ~/.claude. Invisible in the UI; they just run
    the sync twice per session. A hook the user wrote is never touched, even one
    calling `mcpctl skills sync` with different flags.
  - docs/claude-integration.md and docs/prime-agent-extension.md, the two
    integrations that had no page.

prime-agent deliberately keeps its per-project MCP entry name rather than the
constant `mcpctl` claude and opencode now use: its switcher already unmounts the
previous project, so it never accumulates entries, and re-keying auth.json from
mcp:<project> to mcp:mcpctl would give up per-project token caching and needs a
migration. Documented as its own change rather than folded in here.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVwuCjuMoA13gmzYEfcrNP

docs/claude-integration.md

@@ -0,0 +1,114 @@
+# mcpctl × Claude Code
+
+## What `mcpctl config claude --project X` wires up
+
+| Piece | Where | Purpose |
+|-------|-------|---------|
+| MCP entry | `./.mcp.json` | one server, always named `mcpctl`, running the stdio bridge `mcpctl mcp -p X` |
+| Project marker | `./.mcpctl-project` | what `skills sync` reads to know the scope (`--skip-marker` opts out) |
+| Skills | `~/.claude/skills/` | the project's `SKILL.md` bundles |
+| SessionStart hook | `~/.claude/settings.json` | `mcpctl skills sync --quiet` on every session |
+| Status line | `~/.claude/settings.json` | the active project, bottom of the screen |
+| `/mcpctl` | `~/.claude/commands/mcpctl.md` | switch projects from inside a session |
+
+`--claude-dir` (or Claude Code's own `CLAUDE_CONFIG_DIR`) redirects everything
+under `~/.claude`.
+
+## One server named `mcpctl`, not one per project
+
+The MCP entry used to be named after the project. Because `.mcp.json` is
+*merged*, configuring a second project left the first mounted too — every
+project you had ever configured stayed connected, with duplicate tool names and
+nothing marking which was active.
+
+There is now exactly one entry, `mcpctl`, and switching rewrites what sits
+behind it:
+
+```jsonc
+{ "mcpServers": { "mcpctl": { "command": "mcpctl", "args": ["mcp", "-p", "docmost"] } } }
+```
+
+Two things follow. The tool prefix is stable across switches, so the model never
+sees a tool namespace disappear mid-conversation. And because Claude Code can
+reconnect an existing MCP server from `/mcp`, a switch lands without restarting
+the app.
+
+Entries an older CLI wrote are retired on the next run. They are recognised by
+the pairing that makes retiring them safe — *our* command, named after the very
+project it bridges to. A hand-configured server is never touched, even one
+called `docmost`, unless it also runs `mcpctl mcp -p docmost`, at which point it
+is the same entry anyway.
+
+## Switching: `/mcpctl`
+
+```
+❯ /mcpctl docmost
+● Bash(mcpctl config claude --project docmost --skip-marker)
+  ⎿  Wrote .mcp.json (1 server(s))
+● Now on docmost. Reconnect the mcpctl server from /mcp for its tools to load.
+```
+
+With no argument it lists the projects and asks.
+
+Claude Code slash commands are **prompt files, not code**, so unlike opencode's
+picker this drives the model through CLI calls — there is no keyboard picker to
+be had. `allowed-tools` is scoped to the four exact `mcpctl` invocations it
+needs, so accepting it does not hand the session a general shell.
+
+> Every `` !`…` `` block in a slash command is permission-checked against
+> `allowed-tools` *before* the model runs. Omitting one fails the whole command
+> with a permission error and no explanation. A test asserts every pre-executed
+> command in ours is covered.
+
+`--skip-marker` is deliberate: the session's directory is whatever you happened
+to open, and re-scoping it would silently change which skills sync into it.
+
+## The status line
+
+```
+  mcpctl:docmost
+  ⏵⏵ bypass permissions on · ← for agents
+```
+
+`mcpctl statusline` resolves the project from `.mcp.json`, falling back to a
+`.mcpctl-project` marker up the tree so a checkout that is scoped but not yet
+wired still reports. It reads the directory from the JSON Claude Code pipes in,
+so it follows `/cwd` rather than reporting wherever the binary was launched, and
+prints **nothing** when no project is active — an empty status line beats one
+saying "none" on every unrelated repo.
+
+### It is never installed over yours
+
+A status line is a single slot, so overwriting a custom one silently deletes
+work. When `config claude` finds a foreign one it leaves it and prints the
+snippet to add instead:
+
+```
+Left your existing status line alone (my-fancy-prompt).
+  To show the project too, append: $(mcpctl statusline)
+```
+
+> **Ownership is decided by the command string, not a marker.** Claude Code
+> rewrites `settings.json` against its own schema and **strips unknown keys from
+> `statusLine`** — a tagged entry comes back as a bare `{type, command}`.
+> (Hooks keep their marker; `statusLine` does not.) Matching on the command is
+> what stops us reporting our own line as foreign forever. A line that merely
+> *composes* ours — `my-prompt && mcpctl statusline` — is yours, and is left
+> alone.
+
+## Skills
+
+`mcpctl skills sync` installs into `~/.claude/skills/`. Claude Code is the only
+target that also gets hooks, `postInstall` and `mcpServers` auto-attach; pi,
+prime-agent and opencode share the simpler flat-tree semantics.
+
+The SessionStart hook keeps them current. It carries a `_mcpctl_managed` marker,
+and an install now also drops **untagged duplicates of that exact command** —
+rows left behind before the marker existed (or by a test suite that used to
+write into a real `~/.claude`). They are invisible in the UI and just run the
+sync twice per session. A hook you wrote is never touched, even one that also
+calls `mcpctl skills sync` with different flags.
+
+## Running Claude Code on the homelab LLM
+
+See [claude-vllm.md](claude-vllm.md).