PC-0 turns a leading-newline dispatch value into a silent EMPTY_DISPATCH halt #1835

Follow-up nit from FIDO's pass-3 review of #1832 (merged). Filed rather than fixed in-PR because the review verdict was APPROVE/merge-as-is and the path is not reachable from either real producer.

Measured

workflows/squad.md, Step PC-0, normalizes the dispatched command with an awk program gated on NR==1:

printf '%s\n' "$SQUAD_DISPATCH_COMMAND" | awk 'NR==1{sub(/\r$/,""); sub(/^[[:space:]]+/,""); sub(/[[:space:]]+$/,""); if($0==""){print "EMPTY_DISPATCH"; exit} if($0 ~ /^\/squad([[:space:]]|$)/) print; else print "/squad " $0}'

Because the program only ever inspects record 1, a value whose first character is a newline puts an empty string on that record:

PC0($'\nimplement')  →  EMPTY_DISPATCH

EMPTY_DISPATCH routes to the activation guard, which halts with a ::warning:: and no comment — by design, so that empty activation probes stay side-effect free (PR #1777, junk issues #12/#14). So a structurally valid implement dispatch would halt silently rather than run.

Silent-halt-on-valid-input is the same defect class #1824 and #1832 exist to close.

Why this is a nit and not a defect

FIDO enumerated the producers that can reach PC-0:

1. workflows/squad-implement-worker.md:259 — relays a literal single-token value ("command": "implement").
2. The workflow_dispatch UI input — single-line by schema.

Neither can emit a leading newline. Reaching this requires a crafted actions: write API payload, and an actor holding actions: write has strictly larger capabilities available already. FIDO marked the mechanism real but unreachable, and untested.

Suggested fix

Scan the first non-empty line instead of record 1, so leading blank lines are skipped rather than treated as an empty command. Keep EMPTY_DISPATCH for genuinely empty/whitespace-only input.

Add a test alongside the existing PC-0 cases in test/gh-aw-command-parse.test.ts. Per the standing bar, the test must be mutation-proven capable of failing, and its failure message must name the offending input — a status-only assertion would pass a truncating parser.

Acceptance

1. PC0($'\nimplement') yields /squad implement.
2. PC0('') and PC0(' ') still yield EMPTY_DISPATCH.
3. Reverting the fix turns the new test red, and the failure text names the input.
4. Existing PC-0 cases (idempotent prefix, whitespace trim, empty dispatch) stay green, and the load-bearing PC-1 cases (indented, mid-sentence) are untouched.

Source: FIDO pass-3, probe A — https://github.com/bradygaster/squad/pull/1832#issuecomment-5383877533