[Bugfix #562] Require --amends for --protocol tick

[waleedkadous]

Summary

Fixes #562

When af spawn 5 --protocol tick is run without --amends, the specLookupId falls back to the issue number instead of the spec being amended. This causes the builder to read the wrong spec file.

Root Cause

In spawn.ts, the spec lookup logic uses a conditional:

const specLookupId = (protocol === 'tick' && options.amends)
  ? String(options.amends)
  : projectId;

When --amends is omitted, specLookupId defaults to projectId (the issue number), which resolves a different spec than intended. There was no validation requiring --amends for TICK protocol.

Fix

Added validation in validateSpawnOptions() that --protocol tick requires --amends <spec-number>. This is the minimal Option A from the issue — fail fast with a clear error message rather than silently resolving the wrong spec.

Test Plan

• Added regression test: --protocol tick without --amends returns error
• All 106 existing spawn tests pass
• Verified fix locally

[waleedkadous]

Architect Review

Low-risk bugfix. Adds bidirectional validation: --amends already required --protocol tick, now --protocol tick also requires --amends. Clean error message, regression test included.

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Architect review