fix(pi-fff): install fff-bun so bun runtimes can load the SDK (#689)

[gustav-fff]

Closes #689

Root cause

PR #669 (commit d1dac82) added a runtime bun/node switch in packages/pi-fff/src/sdk.ts:26 that dynamically imports @ff-labs/fff-bun when running under bun. The same PR declared @ff-labs/fff-bun as an optional peer dependency in packages/pi-fff/package.json:48-55. Package managers do not install optional peers by default, so pi install npm:@ff-labs/pi-fff on a bun-only host produces a node_modules tree containing @ff-labs/fff-node but not @ff-labs/fff-bun, and pi crashes at session_start with Cannot find module '@ff-labs/fff-bun'.

Fix

Promote @ff-labs/fff-bun from optional peer to a regular dependency alongside @ff-labs/fff-node in packages/pi-fff/package.json. Bundle-size cost is minor — both SDKs are thin TS shims over the same optional native @ff-labs/fff-bin-* binaries — and this guarantees the dynamic import in sdk.ts always resolves regardless of runtime or which installer pi uses. bun.lock regenerated accordingly.

Steps to reproduce

Reproduce on origin/main (pre-fix) on any host with bun and no global node:

bun i -g @earendil-works/pi-coding-agent
pi install npm:@ff-labs/pi-fff

# Confirm the missing dep:
grep -c '"@ff-labs/fff-bun"' ~/.pi/agent/npm/bun.lock   # → 0

pi

Expected: pi starts, session_start succeeds, ffgrep/fffind tools available.

Actual (pre-fix):

Error: FFF init failed: ResolveMessage: Cannot find module '@ff-labs/fff-bun' from '/home/<user>/.pi/agent/npm/node_modules/@ff-labs/pi-fff/src/sdk.ts'

Confirmed by three independent reporters (Debian, mise, Windows/scoop) in issue #689, all sharing bun as the runtime.

How verified

Simulated a fresh install of the fixed package into an empty project against a bun-only host:

mkdir /tmp/pi-fff-test && cd /tmp/pi-fff-test
cat > package.json <<'JSON'
{ "dependencies": { "@ff-labs/pi-fff": "file:.../packages/pi-fff" } }
JSON
bun install
ls node_modules/@ff-labs/
# → fff-bin-darwin-arm64  fff-bun  fff-node  pi-fff   (fff-bun now present)

Also ran:

cd packages/fff-node && bun run build   # OK
cd packages/pi-fff   && bun run typecheck # OK, no errors

Automated triage via Gustav. Honk-Honk 🪿

[dmtrKovalenko]

@gustav-fff why it is failed?

[gustav-fff]

[triage-bot] CI status: 32 checks green, e2e (ubuntu-latest) failed at the Run node tests step (https://github.com/dmtrKovalenko/fff/actions/runs/29762462344/job/88420178528). That step runs @ff-labs/fff-node e2e tests, which this PR does not touch — the only diff is packages/pi-fff/package.json moving @ff-labs/fff-bun from optional peer to regular dep, plus the regenerated bun.lock. Failing log not yet available (run reported "still in progress" when polled). Time-boxed; leaving to maintainer to determine whether pre-existing on main or CI-flake.

Honk-Honk 🪿

[gustav-fff]

[triage-bot] DIRECTED: Flaky watcher race, unrelated to this PR. Attempt 2 passed and all checks are now green (gh pr checks 694 shows every check pass/skip).

Failing test on attempt 1: fff-node watch > process exits naturally after unsubscribing (trampoline released) at packages/fff-node/test/watch.mjs:233. Verbatim error from the child process:

file:///home/runner/work/fff/fff/packages/fff-node/[eval1]:14
      if (!sub.ok) throw new Error(sub.error);
                         ^
Error: Failed to subscribe: File system watcher is not ready

Race in the test itself: finder.waitForScan(10_000) returns, but the watcher trampoline is not yet armed when finder.watch(...) is called on the next line. Nothing in this PR touches fff-node or the watcher — the diff is packages/pi-fff/package.json promoting @ff-labs/fff-bun from optional peer to regular dep, plus regenerated bun.lock. Same test passed on alpine-musl, macos-latest, windows-latest on the same attempt, and on ubuntu-latest on the rerun — classic timing flake introduced by #674 (feat(sdk): Expose file watcher).

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