fix(mosaic): stop yolo runtime from leaking runtime name as first user message

`mosaic yolo <runtime>` forwarded `cmd.args` (which Commander populates with
the declared `<runtime>` positional) to the underlying CLI. For the claude
runtime that meant argv included the literal string "claude" as an initial
positional argument, which Claude Code interpreted as the first user message.
As a secondary consequence, the mission-auto-prompt path was also bypassed
because `hasMissionNoArgs` saw a non-empty args list.

Refactor the runtime subcommand wiring into an exported
`registerRuntimeLaunchers(program, handler)` factory with a
`RuntimeLaunchHandler` type so the commander integration is unit-testable
without spawning subprocesses. Slice the declared positional off `cmd.args`
in the yolo action before forwarding.

Adds `packages/mosaic/src/commands/launch.spec.ts` with 11 regression tests
covering all four runtimes (claude, codex, opencode, pi) for both `<runtime>`
and `yolo <runtime>` paths, excess-args forwarding, and invalid-runtime
rejection. The critical assertion blocks the regression: yolo parses must
forward `extraArgs = []`, not `[runtime]`.

Fixes mosaicstack/stack#454

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/scratchpads/yolo-runtime-initial-arg-20260411.md

@@ -0,0 +1,108 @@
+# Hotfix Scratchpad — `mosaic yolo <runtime>` passes runtime name as initial user message
+
+- **Issue:** mosaicstack/stack#454
+- **Branch:** `fix/yolo-runtime-initial-arg`
+- **Type:** Out-of-mission hotfix (not part of Install UX v2 mission)
+- **Started:** 2026-04-11
+
+## Objective
+
+Stop `mosaic yolo <runtime>` from passing the runtime name (`claude`, `codex`, etc.) as the initial user message to the underlying CLI. Restore the mission-auto-prompt path for yolo launches.
+
+## Root cause (confirmed)
+
+`packages/mosaic/src/commands/launch.ts:779` — the `yolo <runtime>` action handler:
+
+```ts
+.action((runtime: string, _opts: unknown, cmd: Command) => {
+  // ... validate runtime ...
+  launchRuntime(runtime as RuntimeName, cmd.args, true);
+});
+```
+
+Commander.js includes declared positional arguments in `cmd.args`. For `mosaic yolo claude`:
+
+- `runtime` (destructured) = `"claude"`
+- `cmd.args` = `["claude"]` — the same value
+
+`launchRuntime` treats `["claude"]` as excess positional args, and for the `claude` case that becomes the initial user message. As a secondary consequence, `hasMissionNoArgs` evaluates false, so the mission-auto-prompt path is bypassed too.
+
+## Live reproduction (intercepted claude binary)
+
+```
+$ PATH=/tmp/fake-claude-bin:$PATH mosaic yolo claude
+[mosaic] Launching Claude Code in YOLO mode...
+argv[1]: --dangerously-skip-permissions
+argv[2]: --append-system-prompt
+argv[3] (len=25601): # ACTIVE MISSION — HARD GATE ...
+argv[4]: claude                                       ← the bug
+```
+
+Non-yolo variant `mosaic claude` is clean:
+
+```
+argv[1]: --append-system-prompt
+argv[2]: <prompt>
+argv[3]: Active mission detected: MVP. Read the mission state files and report status.
+```
+
+## Plan
+
+1. Refactor `launch.ts`: extract `registerRuntimeLaunchers(program, handler)` with an injectable handler so commander wiring is testable without spawning subprocesses. `registerLaunchCommands` delegates to it with `launchRuntime` as the handler.
+2. Fix: in the `yolo <runtime>` action, pass `cmd.args.slice(1)` instead of `cmd.args`.
+3. Add `packages/mosaic/src/commands/launch.spec.ts`:
+   - Failing-first reproducer: parse `['node','x','yolo','claude']` and assert handler receives `extraArgs=[]` and `yolo=true`.
+   - Regression test: parse `['node','x','claude']` asserts handler receives `extraArgs=[]` and `yolo=false`.
+   - Excess args: parse `['node','x','yolo','claude','--print','hi']` asserts handler receives `extraArgs=['--print','hi']` (with `--print` kept because `allowUnknownOption` is true).
+   - Excess args non-yolo: parse `['node','x','claude','--print','hi']` asserts `extraArgs=['--print','hi']`.
+   - Reject unknown runtime under yolo.
+4. Run typecheck, lint, format:check, vitest for `@mosaicstack/mosaic`.
+5. Independent code review (feature-dev:code-reviewer subagent, sonnet tier).
+6. Commit → push → PR via wrappers → merge → CI green → close issue #454.
+7. Release decision (`mosaic-v0.0.30`) deferred to Jason after merge.
+
+## Framework compliance sub-findings (out-of-scope; to capture in OpenBrain after)
+
+- `~/.config/mosaic/tools/git/issue-create.sh` uses `eval` on `$BODY`; arbitrary bodies with backticks, `$`, or parens break catastrophically.
+- `gitea_issue_create_api` fallback uses `curl -fsS` without `-L`; after the `mosaicstack/mosaic-stack → mosaicstack/stack` rename, the API redirect is not followed and the fallback silently fails.
+- Local repo `origin` remote still points at old `mosaic/mosaic-stack.git` slug. Not touched here per git-config safety rule.
+- `~/.config/mosaic/TOOLS.md` referenced by the global load order but does not exist on disk.
+
+These will be captured to OpenBrain after the hotfix merges so they don't get lost, and filed as separate tracking items.
+
+## Progress checkpoints
+
+- [x] Branch created (`fix/yolo-runtime-initial-arg`)
+- [x] Issue #454 opened
+- [x] Scratchpad scaffolded
+- [x] Failing test added (red)
+- [x] Refactor + fix applied
+- [x] Tests green (launch.spec.ts 11/11)
+- [x] Baselines green (typecheck, lint, format:check, vitest — pre-existing `uninstall.spec.ts:138` failure on branch main acknowledged, not caused by this change)
+- [x] Code review pass (feature-dev:code-reviewer, sonnet — no blockers)
+- [ ] Commit + push
+- [ ] PR opened
+- [ ] CI queue guard cleared
+- [ ] PR merged (squash)
+- [ ] CI green on main
+- [ ] Issue #454 closed
+- [ ] Scratchpad final evidence entry
+
+## Tests run
+
+- `pnpm --filter @mosaicstack/mosaic run typecheck` → green
+- `pnpm --filter @mosaicstack/mosaic run lint` → green
+- `pnpm --filter @mosaicstack/mosaic exec prettier --check "src/**/*.ts"` → green
+- `pnpm --filter @mosaicstack/mosaic exec vitest run src/commands/launch.spec.ts` → 11/11 pass
+- `pnpm --filter @mosaicstack/mosaic exec vitest run` → 270/271 pass (1 pre-existing `uninstall.spec.ts:138` EACCES failure, confirmed on the branch before this change)
+- `pnpm typecheck` (repo) → green
+- `pnpm lint` (repo) → green
+- `pnpm format:check` (repo) → green (after prettier-writing the scratchpad)
+
+## Risks / blockers
+
+None expected. Refactor is small and the Commander API is stable. Test needs `exitOverride()` to prevent `process.exit` on invalid runtime.
+
+## Final verification evidence
+
+(to be filled at completion)