fix(pstack): handle tiny known bug fixes inline

[zhanfeng-alpha]

Why

Tiny fixes with an established mechanism should not require investigation or implementation fanout. Let the parent make and verify these changes inline.

Scope

• Add a known-mechanism, one-predicate or few-line inline fast path.
• Give that path precedence over general fanout triggers.
• Retain Cursor-native subagent_type routing and the existing full scientific path.

Blast Radius

Only the tiny known-mechanism path changes. It still requires a focused repro and relevant checks. Pi-specific profile policy stays in alienczf/pi-stack#8 and is not part of this Cursor plugins change.

Verification

Reverted the Pi-only routing commit. The complete branch tree now exactly matches 29ba8ad, which introduced only the inline fast path. Both changed files were compared byte-for-byte against that commit. Git whitespace checks passed.
The Pi overlay remains unchanged and its native discovery check still returns only poteto-agent. Zero children or supervisor calls were made.

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

^{Bugbot Autofix is ON, but it could not run because the branch was deleted or merged before autofix could start.}

^{Reviewed by Cursor Bugbot for commit 67b8ddd. Configure here.}