ottyl/tickets/034-params-declaration-ui.md

034 — Params declaration UI

Summary

POST /api/params (ticket 004) already lets a param be declared — name, message_match_regex, capture_group, kind — and GET /api/params (fetchParams, webapp/src/lib/api.ts:245) already feeds LogPreview's "Columns" picker (webapp/src/components/LogPreview.tsx:63) so a declared param can be shown as a log table column. But nothing in the webapp can create one — the only way to declare a param today is a raw POST /api/params call. Add a UI for it, following the same declare-then-list pattern Metrics already uses for POST /api/metrics (webapp/src/components/Metrics.tsx).

Scope

• A "Params" section in the primary UI (alongside Log viewer / Metrics / Dashboards in App.tsx), listing currently-declared params (name, regex, capture group, kind) via fetchParams.
• A declare form: name, message_match_regex, capture_group, kind (string/number/timestamp — mirror MetricPrimitiveKind), submitting via a new declareParam call to POST /api/params.
• Surface 400 validation errors from the backend (bad regex, unknown capture group) inline on the form, matching how Metrics' declare form reports its own validation errors.
• After a successful declare, refresh the params list so it (and LogPreview's Columns picker) immediately reflects the new param without a page reload.
• Contextual "?" help icon on the section, matching 021's pattern.

Acceptance criteria

• A param can be declared from the UI and immediately appears in LogPreview's Columns picker without a page reload.
• An invalid regex or unknown capture group shows the backend's error message on the form instead of failing silently.
• The declared-params list matches GET /api/params after a page reload.

Depends on

• 021 — Docs contextual help