Stacked on #230.

Operators can now give the atomic Planner extensions and workflows without installing them into the server's Atomic agent directory. Today the Planner only sees what the agent directory and a verified checkout's `.atomic/settings.json` install, so a package an operator loads with `atomic --extension` in their own terminal never reaches it.

## What changes

- **`HARNESS_EXTENSIONS`.** A list of extension or package paths, separated by the platform path delimiter, that every atomic Planner session loads the same way Atomic's `--extension` flag does. A package's extensions, skills, and workflows all register. Chopin passes the paths to Atomic's resource loader as `additionalExtensionPaths`. - **Startup checks.** Every path must be absolute and must exist. Setting the variable under any other harness refuses at startup. The startup line lists the paths. - **Workers stay isolated.** Background summary and research workers never load these paths. - **Docs.** `self-hosting.md`, `hosted-agent.md`, and `.env.example` describe the variable.

## Verification

- `bun test`: 1907 pass, 2 PostgreSQL skips, 0 fail. The new Planner test registers a local package's tool, skill, and workflow through the operator paths, confirms a worker session on the same harness doesn't see them, and fails without the adapter change. - `bun run types` and `bun run ci` pass. oxlint reports no new warnings and Impeccable no new findings.

## Other changes in this stack

- The composer now shows whether a draft goes to the Planner or only to the room, using the same destination calculation as Send. - Atomic advances to 0.9.27-alpha.1, including workflow-stage questions in Decisions and recovery of durable workflow runs after a session or process fails.

## Extension boundary

Assistant-workflow: inline Assistant-verification: bun test passed: 1907 pass, 2 skip, 0 fail Assistant-verification: bun run types and bun run ci passed Co-authored-by: Alex Lavaee <lavaman131@github.com>


Reviewed the changes against #230: extension-path parsing and startup validation, loading operator packages only in full Planner sessions, worker isolation, and the added composer destination cue. No blocking issues found in this PR’s own diff. Validation, browser integration, and container CI all pass.