feat(do): warn when live-session check fails

[unni-facets]

Today flow do <task> calls liveClaudeSessions() to detect duplicate-tab races before spawning. If ps fails (sandboxed env, broken shim, etc.) the function returns (nil, err) and the live-session guard in internal/app/do.go:176 silently falls through to the spawn path:

if live, err := liveClaudeSessions(); err == nil {
    // ... focus / refuse logic
}

The error is swallowed with no user-visible signal. In environments where ps reliably fails, users will silently see duplicate-spawn behavior with no indication that the safety check was skipped.

Proposed change

When liveClaudeSessions returns a non-nil error, print a single line to stderr before falling through:

warning: live-session check skipped: <error>

Then continue to the spawn path as today. Behavior on the happy path is unchanged.

Files

• internal/app/do.go:175-197 — add the stderr line in the else branch of the err == nil check
• internal/app/do_test.go — extend an existing test (or add one) that stubs psRunner to return an error and asserts the warning is written to stderr

Notes

• Best-effort signal: the check is non-blocking by design, so behavior must NOT change to error-out. Only the stderr surface changes.
• Match the tone of the existing duplicate-process warning at do.go:179.

Acceptance

• go test ./... green
• go vet ./... clean
• Test covering the psRunner error path