fix(workflows): reject a fan-in wait_for that names an unknown step at validation

[doquanghuy]

Description

Closes #3223. Sibling to #2957 (fail loud when a fan-out items expression does not resolve to a list).

A fan-in whose wait_for names a step id that isn't declared — a typo, or a forward reference to a step declared after the fan-in — currently aggregates an empty result and reports COMPLETED, masking the authoring error. validate_workflow now flags it: each wait_for id must name a step declared at or before the fan-in, checked against the seen_ids set _validate_steps already maintains.

A step that is declared but only conditionally executed (e.g. inside an if/switch branch) is still "seen", so a legitimately-empty join stays valid — only genuinely unknown or forward-referenced ids are rejected. This is validation-time, so there is no runtime behavior change for correctly-authored workflows.

Testing

• Ran the workflow suite with .venv/bin/python -m pytest tests/test_workflows.py — 314 passed, including 4 new TestFanInWaitForValidation cases: unknown id rejected, declared-earlier id passes, conditionally-declared (if-branch) id passes, forward reference rejected.
• uvx ruff check src/ tests/test_workflows.py — clean
• Tested locally with uv run specify --help

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Code, tests, and this description were authored with AI assistance (Claude Code), from a fan-out/fan-in audit; everything was verified by running the repo's test suite and ruff locally.

@mnriem — small validation-only change; would appreciate your review when you have a moment.

[Copilot]

Pull request overview

This PR tightens workflow validation to prevent fan-in steps from silently producing empty join results when wait_for references an invalid step id, addressing #3223 and aligning with prior “fail loud” validation work.

Changes:

• Add engine-level validation to ensure fan-in.wait_for only references step ids already declared at the point of the fan-in.
• Add unit tests covering unknown wait_for ids, valid earlier ids, conditionally declared ids, and forward references.

Show a summary per file

File	Description
src/specify_cli/workflows/engine.py	Adds fan-in wait_for validation against already-seen step ids during workflow validation.
tests/test_workflows.py	Adds new test cases asserting validation rejects unknown/forward-referenced wait_for ids and allows earlier/conditional ids.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Low

[doquanghuy]

Thanks @copilot for the review — both points addressed at root cause in d9c867b:

• Self-reference: a fan-in's own id is already in seen_ids by the time wait_for is checked, so wait_for: [<self>] passed validation while still producing a silent empty join at runtime. Now rejected explicitly.
• Non-string entries: wait_for: [123] was skipped by the isinstance(str) guard and silently validated even though it can never match a step id. Now flagged as a wiring error.

Added coverage: test_self_reference_is_rejected, test_non_string_wait_for_entry_is_rejected.

@mnriem would you mind taking a look when you have a moment? 🙏

[Copilot]

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Low

[mnriem]

Thank you!