## What / Why
**Reworked after FN-8179 (`fd43a57a4`) landed on `main`.** FN-8179 did
most of what the original PR #2261 did — pinned `@earendil-works/pi-ai`
/ `pi-coding-agent` to `^0.80.10` everywhere, added the
`createSessionOptions` `NonNullable` typing in `pi.ts`, and regenerated
`pnpm-lock.yaml`. This PR was rebased onto current `origin/main` and
reduced to **only the unique residual not covered by FN-8179**.
### Residual change 1 — defensive `getAuth` guard
The FN-8142 migration rewrote `attachSessionRoutingHeaders` from the
`ModelRegistry.getApiKeyAndHeaders` seam to `ModelRuntime.getAuth`, but
dropped the pre-migration defensive invariant: a missing resolution
method must **not** break session creation. On `main` the function now
calls `modelRuntime.getAuth.bind(...)` unguarded, which throws if
`getAuth` is ever absent.
This restores the guard: no-op (warn) when `getAuth` is missing, so a
future pi rename degrades to un-tagged requests instead of a hard
failure at every agent start.
### Residual change 2 — test realignment (needed against current main)
FN-8179 aligned the SDK but did **not** update the two `#1675`
routing-header test suites, which still asserted the old
`getApiKeyAndHeaders` seam. **Verified RED on current `main` before
touching them:**
- `pi-create-fn-agent.test.ts` — **60 / 104 failing** (mock had no
`ModelRuntime` export; `createAgentSession` now receives
`modelRuntime`).
- `pi-session-routing-headers.test.ts` — **4 / 5 failing**
(`attachSessionRoutingHeaders` signature is `getAuth`, not
`getApiKeyAndHeaders`).
Both are realigned to the `ModelRuntime.getAuth` seam (the mock gains
the `ModelRuntime` export) → **109 / 109 green**. Assertions were
strengthened to the new behavior, not weakened; the #1675 precedence
invariant (taskId > pi session id > no-wrap), header merge,
apiKey/provider-header passthrough, failed/undefined passthrough, and
absent-method no-op are all still asserted.
## Surface enumeration
- **Routing-header seam**: both the `createFnAgent` path and the
`attachSessionRoutingHeaders` unit (taskId / pi-session-id / no-id
precedence; header merge; apiKey + provider-header passthrough;
failed/undefined resolution; absent-method no-op).
- **Both mock forms** in `pi-create-fn-agent.test.ts`: the top-level
`vi.mock` and all three `vi.doMock` skill-selection blocks now export
`ModelRuntime`.
## Test evidence
- `pnpm --filter @fusion/engine exec tsc --noEmit` → **exit 0**.
- `pnpm --filter @fusion/engine exec vitest run` on both suites →
**109/109 pass** (was 64 failing on main).
- `pnpm verify:fast` → **PASS** (typecheck + build scoped to changed
packages + CLI build + boot smoke `GET /api/health 200`; no tests run).
Do not merge without CI. No release performed.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Improved session creation reliability when authentication support is
unavailable.
* Preserved existing authentication details while adding session-routing
headers when supported.
* Prevented session creation from failing when authentication
information cannot be resolved.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Co-authored-by: Claude Opus <noreply@anthropic.com>
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