validate-tasks

Run sh scripts/lint-tasks.sh. The script takes no arguments.

• Exit code 0 means docs/tasks.md is structurally clean.
• Non-zero exit prints one validate: <check>: <detail> line per issue on stderr.

Content checks enforced:

• no duplicate ### Tn.m or ### Sn task headings
• docs/tasks.md contains a ## Execution State section
• ## Execution State has the required labels:
  • Current active task
  • a Next executable product task... label (repo convention: Next executable product task after blocker clearance)
  • Last completed task
  • Completed tasks recorded here
  • Blocked tasks
  • Open deviations
• every Tn.m (product task, optional lowercase suffix) or Sn (spike) reference inside ## Execution State points to a real task heading
• every Open deviations entry other than None recorded includes at least one task ID (Tn.m or Sn)
• every task heading matched by the script has a non-empty task block

Invocation checks (also emitted in the validate: <check>: <detail> format):

• validate: invalid_invocation: ... if any argument is passed (the script takes none)
• validate: tasks_file_missing: <path> if docs/tasks.md cannot be found

Do not modify docs/tasks.md to make the lint pass. Raise any failure as a classified deviation per docs/operating-model.md §10 and escalate to the user.

Return:

1. exit code
2. each stderr line verbatim if any
3. suggested primary classification per docs/operating-model.md §10 for each failure