feat(plan): richer PlanArtifact schema for v0.9.0 (#2691)

crates/tui/src/commands/mod.rs

@@ -1171,6 +1171,7 @@ mod tests {
                     step: "keep checklist primary".to_string(),
                     status: StepStatus::InProgress,
                 }],
+                ..Default::default()
             });
         }
 

crates/tui/src/prompts/modes/plan.md

@@ -8,6 +8,22 @@ the final plan; that is the handoff signal that lets the UI show the accept / re
 All writes and patches are blocked — you can read the world but you
 can't change it. Shell and code execution are unavailable.
 
+Produce a grounded plan artifact through `update_plan`, not just a step list. Include what you
+discovered during investigation so the user can make an informed decision:
+
+- `title` — short summary
+- `objective` — what this plan aims to achieve
+- `context_summary` — what you found during investigation
+- `sources_used` — files, docs, commands, or sub-agents consulted
+- `constraints` — user rules, repo constitution, mode limits, safety constraints
+- `recommended_approach` — high-level approach and rationale
+- `plan` — ordered execution steps with statuses (required)
+- `verification_plan` — how to verify correctness
+- `risks_and_unknowns` — known risks, assumptions, open questions
+- `handoff_packet` — compact summary for Agent-mode execution
+
+All fields except `plan` are optional — only include what you actually discovered.
+
 Use this mode to build a thorough plan. Spawn read-only sub-agents for parallel investigation.
 After `update_plan` presents the plan, wait for the user's next action instead of continuing to
 tool around in Plan mode.