feat: in-app config editor (CodeMirror 6 workbench with live impact preview)

[StephenSook]

Summary

Adds an in-app config editor (the ContextMod Observatory workbench) so moderators load, edit, validate, and save their rule config without leaving the dashboard. Replaces the prior "click out to the raw wiki" workflow that FoxxMD flagged as the top friction point in his 2026-05-27 feedback.

What this gives a moderator

Click Edit config in the dashboard. The webview expands. A CodeMirror 6 editor loads the current wiki config with line numbers, YAML/JSON syntax coloring, schema-driven autocomplete + hover docs, and inline AJV validation. Right pane:

• Impact tab runs the FULL config against a cached sample of the sub's real recent posts in dry-run; updates as you type. "Would fire on N/M recent items". Verified 9/9 live during playtest.
• Explain tab calls OpenAI for a plain-English summary of the current config.
• Diff tab shows added/removed lines vs the loaded config.

Save writes back to the wiki via reddit.updateWikiPage, validation-gated (an invalid config can never reach the wiki) and optimistic-locked (refuses with a 409 on a concurrent edit), with the revision reason "Edited via ContextMod Observatory by u/...".

Architecture

• Server (Hono): new src/routes/configEditor.ts exposes GET /api/config/raw, POST /api/config/validate, POST /api/config/simulate-live, POST /api/config/explain, POST /api/config/save. All mod-auth gated, rate-limited where cost-bearing, structured 503 on transient failures.
• Dry-run engine: new simulateFullConfig in src/core/simulateRule.ts runs the whole config per sample with bypassIdempotency: true and forced dryRun: true. Zero real actions can fire (proven structurally and locked by a regression test).
• Client: lazy-loaded ConfigWorkbench (CodeMirror 6 + codemirror-json-schema) so the dashboard main entry stays at 118K with zero CodeMirror in it; the workbench chunk loads only when the editor opens. requestExpandedMode provides the surface.
• Schema: about 120 description fields added to app.schema.json so the editor's hover docs are real, sourced from the JSDoc on the TypeScript rule/action/filter interfaces.

Verification chain

• Unit + component tests: 896 passing across 89 files. Type-check and lint clean throughout.
• Per-task two-stage review (spec compliance, then code quality) on every task. Two opus adversarial safety passes:
  • The privileged wiki write: traced the validation gate and the optimistic lock as airtight.
  • The simulate dry-run: confirmed structurally that zero real Reddit actions can fire (early return in runAction before the action switch, when bypassIdempotency: true). Locked with a regression test that spies on all 10 Reddit mutation methods (remove, approve, submitComment, lock, report, banUser, setUserFlair, distinguish) and asserts none are called while firedCount >= 1.
• Final whole-feature coherence review (opus): GO. Caught one important real gap (the headline Impact tab erroring on full configs because /simulate-live reused the single-rule simulateRule); fixed by routing the full config through the dry-run engine and locked with the safety test above.
• Playwright E2E in real chromium: 4/4 pass (opens workbench, CodeMirror visible, three preview tabs present, Impact fire-rate renders, Close hides).
• Live Devvit playtest on r/cm_devvit_test:
  • CodeMirror renders under the real webview CSP. Zero Content-Security-Policy, unsafe-eval, or style-src violations from cm-devvit in the console.
  • Save writes to the wiki successfully: rev incremented from 5 to 7 to 8 to 9 across saves.
  • Live Impact preview reported "Would fire on 8/9" then "9/9" against the sub's real recent posts.
  • requestExpandedMode opens the editor in expanded mode.

Follow-ups (out of scope for this PR)

1. Download is disallowed ... frame ... sandboxed in the playtest console: the Devvit webview iframe lacks the allow-downloads sandbox flag, so the pre-existing Export CSV button's programmatic download is blocked. Either request allow-downloads from Devvit, or replace Export CSV with a copy-to-clipboard fallback. Not introduced by this PR.
2. OpenAI quota. The Explain tab will surface "OpenAI HTTP 429: quota exceeded" until billing is topped up on the configured key. The endpoint correctly surfaces this as an inline error; not a code bug.

Commits

19 atomic commits on this branch (git log --oneline 9700f4d..HEAD), grouped by plan phase:

• Phase 1 (server): resolveOpenaiKey extract, getRecentSample cached extract, raw, validate, simulate-live, explain, save, error-branch hardening.
• Phase 2 (client): CodeMirror deps, API helpers, ConfigEditor (CM6 + schema), ConfigWorkbench + lazy-load + expanded-mode wiring.
• Phase 3 (schema): description fields for editor hover docs.
• Phase 4 (preview): PreviewPane (Impact / Explain / Diff), workbench split layout, ARIA + comment polish.
• Phase 5 (verification + fixes): demo-mode mock-server handlers, Playwright E2E, the simulate-live full-config fix, the dry-run safety regression test.

Design spec: docs/superpowers/specs/2026-05-27-config-editor-design.md.
Implementation plan: docs/superpowers/plans/2026-05-27-config-editor.md.

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