feat: show each step's output contract in the workbench detail pane

[tylerdavis]

What

Selecting a step in the plan workbench showed its input template but nothing about what the tool returns. Now the detail pane shows the tool's output contract under the input template, using the same precedence the context tab already had:

• the tool's declared output_schema, else
• the observed output shape + example recorded from prior runs,
• plus any declared output example (how control steps like map describe their output).

Once a step has run, the real result replaces the prediction.

Why control steps needed one more change

The workbench loaded its tool context from the registry alone, which deliberately excludes control steps (decide, map, reduce, …) — they're executor-evaluated, never registered. Effect::LoadContext now appends control_step_defs() exactly like graph tools list does, so:

• the context tab truly shows "what the planner sees" (it was silently missing the control vocabulary), and
• map/reduce/decide/agent/ask steps get their declared output examples in the step detail pane.

Verification

• New render tests: shape shown until a result lands; declared schema wins over observed shape; map shows its output example.
• mise run lint + full workspace tests green.
• Docs screenshots regenerated through the shots harness (context-tab catalog count 22 → 29; the control steps sit below the visible window, overview unchanged).
• docs/workbench/plan-workbench.mdx updated in the same PR.

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Note

graph_review_9000 · A focused, well-tested UI-only enhancement to the workbench's plan/context tabs that surfaces a step's output contract and appends control-step defs to the loaded catalog, with matching docs updates.

At a glance

Pass	Area	Status
1	Stated Intent	✅ Pass
2	Pipeline/Control-Step Invariants	⚪ N/A
3	Template/Shape Engine	⚪ N/A
4	Rust/Async/Storage Footguns	✅ Pass
5	Plan Composition/Model Routing	⚪ N/A
6	Test Coverage	✅ Pass
7	Repo Conventions/Docs Parity	✅ Pass
8	CLI Surface/Copy	✅ Pass

🧵 0 new · 0 open · 0 resolved this run · 0 declined

⚪ N/A · ✅ Pass

Stated Intent — Diff matches the stated intent: output-contract precedence added to step detail, control_step_defs appended to LoadContext, docs/screenshots updated.

Pipeline/Control-Step Invariants — Diff is UI-only (workbench rendering + context loading); no changes to gate, error policy, or control-step evaluation semantics.

Template/Shape Engine — No changes to template/, shapes.rs, or store.rs shape cache — this pass doesn't apply.

Rust/Async/Storage Footguns — No new unwrap/panic on reachable paths, no Store bypass, no MCP lifecycle touch; changes are pure data assembly/rendering.

Plan Composition/Model Routing — No touch to plan__* composition, ModelRouter, or provider/failover code.

Test Coverage — New tests cover the precedence order (declared schema > observed shape > example), the result-replaces-prediction transition, and control-step output examples via a workspace mirroring LoadContext's tool mix.

Repo Conventions/Docs Parity — docs/workbench/plan-workbench.mdx and the context-tab screenshot were updated in the same PR to reflect both the new step detail contract and the control-step catalog count.

CLI Surface/Copy — New TUI copy ('output schema', 'observed output shape', 'observed example', 'output example') is consistent with existing section-label conventions in the same file; no stdout/stderr/exit-code paths touched.