missions: retry failed phases + auto-purge on re-launch

Every re-attempted phase now starts with a clean slate:

  - phase_runner::launch_phase DELETEs prior status IN ('failed',
    'cancelled') topology_runs for the phase before enqueuing the
    new ones. Completed runs are kept for audit; only the failure
    noise from earlier attempts goes.
  - POST /api/missions/{id}/phases/{phase_id}/retry — resets a
    failed/cancelled phase to 'pending' (auth-scoped to the calling
    workspace + guarded on mission.status='running'). phase_runner
    picks it up on the next 10s tick.
  - MissionCanvas phase card grows a coral 'Retry' button, visible
    only when phase.status='failed' and mission.status='running'.
    Click → resets + refreshes; the prior failed run rows disappear
    from the card as soon as phase_runner enqueues the new attempt.

Design: auto-purge in phase_runner rather than a separate 'clear
failed runs' endpoint. Users don't have to manually clean up before
retrying; the runner does it as part of the natural work of firing
a fresh attempt.

Verified: cargo check + tsc + eslint --quiet all green.

crates/cm-api/src/routes/missions.rs

@@ -447,6 +447,39 @@ pub async fn list_teams(
     Ok(Json(serde_json::json!({ "teams": teams })))
 }
 
+/// POST /api/missions/{id}/phases/{phase_id}/retry — reset a
+/// failed / cancelled phase back to 'pending' so the phase_runner
+/// picks it up on the next tick. The runner purges old failed
+/// topology_runs for the phase before re-enqueuing, so the phase
+/// card starts fresh on the retry.
+pub async fn retry_phase(
+    State(state): State<AppState>,
+    Authed(user): Authed,
+    Path((id, phase_id)): Path<(Uuid, Uuid)>,
+) -> Result<Json<Value>, ApiError> {
+    // Scope check on the mission.
+    let mission = cm_db::repo::missions::get(&state.pool, id, user.workspace_id.as_uuid())
+        .await?
+        .ok_or(ApiError::NotFound)?;
+    if mission.status != "running" {
+        return Err(ApiError::BadRequest);
+    }
+    let r = sqlx::query(
+        "UPDATE mission_phases
+            SET status = 'pending', started_at = NULL, completed_at = NULL
+          WHERE id = $1 AND mission_id = $2
+            AND status IN ('failed', 'cancelled')",
+    )
+    .bind(phase_id)
+    .bind(id)
+    .execute(&state.pool)
+    .await?;
+    if r.rows_affected() == 0 {
+        return Err(ApiError::NotFound);
+    }
+    Ok(Json(serde_json::json!({ "reset": true })))
+}
+
 /// GET /api/missions/{id}/runs — topology_runs bound to this mission,
 /// newest first. Used by the Live tab to subscribe to per-run SSE.
 pub async fn list_runs(