## Problem
Running a simulation on MLB (and any sport where the readiness check fails) showed a confusing React Router 400 error instead of the real failure reason. The cause: the simulate route had only an \`action\` export. When the action **threw** instead of redirecting, React Router tried to render the route via GET to display the error — hit the missing loader — and replaced the real error with its own internal 400.
A secondary issue: the interim fix used \`?simulationError=\` query params, which had three problems identified in code review:
- Stale errors re-appeared when pressing browser Back after fixing the issue
- The param reflected arbitrary text into the UI (social engineering surface)
- The styling didn't match the established \`bg-destructive/15\` error pattern
## Changes
**\`admin.sports-seasons.\$id.simulate.tsx\`** — strip the action; keep a loader-only redirect stub so bookmarked URLs degrade gracefully to the season page.
**\`admin.sports-seasons.\$id.tsx\`** — add \`intent="simulate"\` to the action dispatcher (matching \`delete\`, \`rescore\`, \`sync-standings\`, \`finalize-standings\`). On success: redirect to expected-values (unchanged). On failure: return \`{ simulateError: message }\` displayed inline with the correct \`bg-destructive/15\` styling.
## Test plan
- [ ] Click Run Simulation on a season with a missing readiness input → error message appears inline below the description text, styled consistently with other errors on the page
- [ ] Click Run Simulation on a fully-configured season → redirects to expected-values as before
- [ ] Navigate directly to \`/admin/sports-seasons/<id>/simulate\` in browser → redirects to season page (no 400)
- [ ] Run simulation, see error, fix the issue, run again successfully → no stale error message persists
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Chris Parsons <chrisparsons1127@gmail.com>
Reviewed-on: #64
chrisp
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