fix: seed task runtime home with the worker mise global config

[mrubens]

Problem

Environment-defined stdio MCP servers (for example npx -y <mcp-package>) never came up in sandboxes. The config pipeline was fine — the servers reached the OpenCode config — but OpenCode marked them server unavailable / status=failed about a second after session create.

Root cause: npx/node in the sandbox are mise shims, and mise resolves tool versions from the global config at $HOME/.config/mise/config.toml when no repo-level mise config applies to the spawn cwd. The harness, agent bash, and MCP subprocesses all run with HOME remapped to the per-task runtime home (<workspace>/.roomote-runtime-home), which starts empty — worker setup's mise use -g nodejs@22 only writes the worker daemon's own home. So in any environment whose repo doesn't pin a node version, the shim fails instantly:

mise ERROR No version is set for shim: node

and the MCP server dies before it can speak MCP. The agent just silently never sees its tools.

Fix

Add seedRuntimeHomeMiseGlobalConfig, called at the HOME-remap point in runTask: it copies the worker home's .config/mise/config.toml into the task runtime home.

• Never clobbers an existing runtime-home config (snapshot resume, or an agent that ran mise use -g itself).
• Best-effort: a copy failure cannot break task startup.
• File-based rather than env-var-based on purpose: MCP children are spawned with a minimal inherited env, so $HOME/.config is the one location that reaches every spawn path. This also fixes agent-bash npx in repos without a pinned node version.

Verification

• Reproduced the failure in a live sandbox (env with a custom npx-based MCP server; OpenCode logged server unavailable key=<name> type=local status=failed, and running the command in agent bash showed the mise shim error).
• With the fix, a fresh task in the same environment loaded the MCP server's tools and the agent successfully invoked them.
• New unit tests for the seeding behavior (seed, no-clobber, missing source, same-home no-op). Full worker suite passes; lint:fast, check-types:fast, and knip pass.

Notes

• Tests that vi.mock('../agent-home') needed the new export stubbed (missing mock exports crash the vitest fork via the run-task crash handler).
• Follow-up (separate task): surface MCP startup failures as a diagnostic event / task-timeline warning instead of only OpenCode's internal log.

[roomote-roomote]

No code issues found. See task

_{Reviewed c782868}