feat(tess): add configurable Pi interaction service (#728)

docs/scratchpads/tess-m2-001-pi-service.md

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+# TESS-M2-001 — Pi Interaction Service
+
+## Scope
+
+- Add a generic rostered/systemd Pi operator-interaction service in
+  `packages/mosaic/framework`.
+- Pin the service to `openai/gpt-5.6-sol`, high reasoning, and the
+  `operator-interaction` tool policy.
+- Keep identity as provisioning data; the product name appears only in the
+  committed example roster.
+
+## Security and Configuration Invariants
+
+1. The chosen display/roster name is supplied as data and must exactly match the
+   generic systemd instance.
+2. The service fails before launch if runtime, model, reasoning, or tool policy
+   differs from the pinned policy.
+3. Effective-policy output includes only name, runtime, model, reasoning, and
+   tool policy; it does not inspect or output credential variables.
+4. The default example is replaceable without a source change; the TDD suite
+   provisions `Nova` from the same profile.
+
+## Evidence
+
+- `src/fleet/tess-service-profile.test.ts` proves a `Nova` provisioning path,
+  roster parser/env serialization, effective-policy output, fail-fast drift
+  rejection, and absence of the product name from generic source/profile.
+- `test-fleet-units.sh` validates the generic interaction systemd unit requires
+  per-agent config and invokes fail-fast startup validation.
+- `test-start-agent-session.sh` proves the tool-policy value is exported into
+  the Pi pane; `compose-contract.spec.ts` proves it becomes an explicit
+  runtime contract block.
+- Fresh-worktree dependency install plus root `pnpm typecheck`, `pnpm lint`,
+  `pnpm format:check`, and `pnpm test` passed; package/full fleet suites passed.
+- Independent Codex code and security reviews passed with no remaining findings.
+
+## Delivery Notes
+
+- Branch starts from fresh `origin/main` at `86a50138`.
+- PR targets `main` and references issue `#708`.