pi-fff: switching modes leaves stale tool names active after `/reload`

[RunMintOn]

Summary

registerPendingTools only ever adds names to the active tool set, never removes old ones. After switching from override back to a FFF-named mode and running /reload, the restored active list still contains the previous mode's tool names, so the model sees duplicate search tools.

Per the README, override replaces the built-in find / grep, and switching modes takes effect after /reload when the tools are registered again. The stale names contradict both statements.

Reproduction

1. Start Pi with pi-fff in override mode (grep / find active).
2. Run /fff-mode tools-and-ui, then /reload.
3. Check the active tools (e.g. via /tool or the model's tool list).

Actual

Stale search tools stay active alongside the final mode's names: grep, find, ffgrep, fffind (functionally duplicated in pairs).

Expected

The active set matches the final mode: only ffgrep / fffind (plus fff-multi-grep when enabled).

Verification (two-session mock on #854's branch)

Fresh extension instance per reload, one shared persisted active list:

direction	active set after reload	status
default -> override	read, grep, find	fixed by #854's prune
override -> default	read, grep, find, ffgrep, fffind	still open (this issue)

Notes

• The default-to-override direction was fixed as a side effect of fix(pi-fff): preserve FFF tool renderers across reload #854's prune: pre-registered FFF names are instance-tracked, so they are removed from the active set.
• Fresh sessions are unaffected in either direction.
• A fix needs to distinguish the extension's grep / find registrations from Pi's built-ins sharing those names (e.g. via getAllTools source info), so it is kept out of fix(pi-fff): preserve FFF tool renderers across reload #854.

[gustav-fff]

[triage-bot] REPRODUCED: Reproduced on origin/main. Branch: triage-bot/issue-855.

registerPendingTools is purely additive (packages/pi-fff/src/index.ts:659-665), and pi carries the pre-reload active list into the rebuilt registry (dist/core/agent-session.js:2063 passes activeToolNames: this.getActiveToolNames()). So the previous mode's names stay active.

Both directions still reproduce on main, not only override -> default. Note pi's default active set is ["read", "bash", "edit", "write"] (dist/core/sdk.js:132) — builtin grep/find ship inactive, so leftover grep/find in a FFF-named mode really are the extension's stale activations, not user intent.

Repro via the regression test (fails on pre-fix main, passes on the branch):

cd packages && bun install --frozen-lockfile
git checkout triage-bot/issue-855 -- pi-fff/test/extension.test.ts
cd pi-fff && bun test test/extension.test.ts

(fail) pi-fff mode switch across /reload > drops override tool names when switching back to a FFF-named mode
(fail) pi-fff mode switch across /reload > drops FFF tool names when switching to override
 26 pass
 2 fail

Expected active after override -> tools-and-ui + /reload: ["read","bash","edit","write","ffgrep","fffind"].
Actual: ["read","bash","edit","write","grep","find","ffgrep","fffind"].

Working on fix on triage-bot/issue-855.

Honk-Honk 🪿