test(repro): skip repro-flow-execute when local session file is absent

[PhucHai123]

Problem

tests/repro-flow-execute.test.ts relies on a hardcoded session fixture path that only exists on one developer's machine:

/Users/__blitzzz/.pi/agent/sessions/--Users-__blitzzz-Documents-GitHub-pi-agent-flow--/2026-06-19T03-30-34-480Z_019eddee-2d70-71a0-9a21-cdc21b692771.jsonl

When CI (or anyone else) runs npm test, the file is missing and the suite fails with:

Error: ENOENT: no such file or directory, open '/Users/__blitzzz/.pi/agent/sessions/...'

Fix

Make the repro test conditional on the fixture being present:

it.skipIf(!fs.existsSync(SESSION), "bare scout (no dispatch) does not throw 'length'")(async () => {

The test still runs locally when PI_REPRO_SESSION points at an existing file, but it no longer breaks CI or other contributors' machines.

Scope

This is a CI hygiene fix. It is split out from #36 so that PR can remain focused on the withFileMutationQueue install fix.

Suggested merge order: merge this PR first, then #36 will pass CI cleanly.