fix: show step name in tree view for forEach-expanded steps

[stack72]

Summary

Fixes #867 — forEach-expanded steps in the workflow tree view now show the step name as a prefix when it differs from the model name.

Before:

test
  ├─ tester → smokeTest    ∴ 1.9s
  ├─ tester → smokeTest    ∴ 1.9s
  ├─ tester → smokeTest    ∴ 1.9s

After:

test
  ├─ test-alpine: tester → smokeTest    ∴ 1.9s
  ├─ test-discord: tester → smokeTest   ∴ 1.9s
  ├─ test-github: tester → smokeTest    ∴ 1.9s

What changed

Three label construction sites in the tree view renderer were updated to prefix the step ID when stepId !== modelName:

• step_line.tsx — live expanded step labels
• job_line.tsx — inline single-running-step labels
• state.ts — graduated scrollback labels after job completion

Why this is correct

• The domain layer already propagates the correct expanded step name (e.g., test-alpine) as the stepId through workflow events — this is purely a presentation fix
• The prefix is only added when stepId !== modelName, so non-forEach steps where the step name naturally matches the model name (e.g., ec2-instance → create) remain unchanged
• The --json output and report system already had the correct step names — this brings the tree view in line with those

User impact

Users running workflows with forEach steps can now tell which iteration is which during live execution, without the workaround of creating N separate model instances per iteration.

Test Plan

• Updated existing scrollback label assertion to account for the new prefix format
• Added test: forEach-expanded step with stepId !== modelName shows "test-alpine: tester → smokeTest"
• Added test: regular step with stepId === modelName shows "ec2-instance → create" (no prefix)
• All 39 tests in workflow_run_tree/ pass
• Full deno check, deno lint, deno fmt pass

🤖 Generated with Claude Code

[github-actions]

CLI UX Review

Blocking

None.

Suggestions

None.

Verdict

PASS — Clean presentation fix. The step-name: model → method format is clear and scannable, the prefix is correctly suppressed when stepId === modelName (preserving existing non-forEach output), and all three label construction sites are updated consistently. JSON output was already correct; this brings the tree view in line.

[github-actions]

Code Review

Presentation-only fix that's well-scoped and correctly implemented. All three label construction sites (step_line.tsx, job_line.tsx, state.ts) apply the same stepId !== modelName prefix logic consistently. The domain layer already had the right data — this just surfaces it in the tree view.

Blocking Issues

None.

Suggestions

1. The label construction logic (modelMethod + conditional stepPrefix) is duplicated across three files. A small shared helper (e.g., formatStepLabel(stepId, modelName, methodName)) would reduce the duplication, but this is minor given the simplicity of the logic and not worth blocking on.

DDD: Changes are purely presentation-layer — no domain logic modified. ✓
Imports: All libswamp imports go through mod.ts. ✓
Tests: Two new tests cover the forEach-expanded prefix case and the no-prefix case; existing test updated to match the new behavior. ✓
License headers: Present on all files. ✓
Code style: No any types, named exports used. ✓