Add bulk clear-params action that re-extracts from retained logs (ticket 052)

DELETE /api/params clears the entire standalone-param set — manual and
auto-derived alike — then immediately re-runs auto_declare_params against
every IndexKey::IngestedLog entry still held in the engine's index (oldest
to newest), so params come back fresh from currently-retained log text
without requiring new lines to be ingested. This is a deliberate full
reset, unlike reload_engine_declarations's profile-switch cleanup, which
preserves auto-derived params since those are engine-discovered facts
rather than profile state; here the immediate re-extraction step makes
clearing them safe.

Settings::clear_param_declarations empties the active profile's persisted
params so they don't reappear on restart. The webapp's Params section gets
a single "Clear all" button (with a confirm dialog and a status line
reporting removed/re-derived/logs_considered) rather than a per-param
delete loop; logs_considered surfaces that lines already evicted by
max_logs can't regain their params.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/components/Params.tsx

@@ -1,5 +1,5 @@
 import { useMemo, useState } from 'react'
-import { ApiError, declareParam, type ParamDeclaration } from '../lib/api'
+import { ApiError, clearParams, declareParam, type ParamDeclaration } from '../lib/api'
 import {
   CollapseToggle,
   handleSectionHeaderKeyDown,
@@ -48,6 +48,9 @@ export function Params({ params, onDeclared }: { params: ParamDeclaration[]; onD
   // in place by name, so changing it here would silently create a second param and orphan the
   // original (and anything referencing it by name) rather than renaming it.
   const [editingName, setEditingName] = useState<string | null>(null)
+  const [clearing, setClearing] = useState(false)
+  const [clearResult, setClearResult] = useState<string | null>(null)
+  const [clearError, setClearError] = useState<string | null>(null)
 
   const isBoolean = kind === 'boolean'
   const isElapsedSinceLast = source === 'elapsed_since_last'
@@ -117,6 +120,33 @@ export function Params({ params, onDeclared }: { params: ParamDeclaration[]; onD
     }
   }
 
+  // Clears every declared param (manual and auto-derived) in one action, then immediately
+  // re-derives whatever the engine can still find in retained log text (ticket 052) — a single
+  // confirmed click rather than removing params one at a time. `logs_considered` in the response
+  // is surfaced in the status line so it's clear the re-extraction only covers logs the engine
+  // still holds, not ones already evicted by a max-logs cap.
+  async function handleClearAll() {
+    if (params.length === 0) return
+    if (!window.confirm(`Clear all ${params.length} declared param(s)? Params will immediately be re-derived from log lines still held in memory; lines already evicted by a log cap can't regain their params.`)) {
+      return
+    }
+    setClearing(true)
+    setClearError(null)
+    setClearResult(null)
+    try {
+      const result = await clearParams()
+      setClearResult(
+        `Cleared ${result.removed}, re-derived ${result.reextracted} from ${result.logs_considered} retained log line(s).`,
+      )
+      resetForm()
+      onDeclared()
+    } catch (err) {
+      setClearError(err instanceof ApiError ? err.message : 'Failed to clear params')
+    } finally {
+      setClearing(false)
+    }
+  }
+
   return (
     <div className="border-b border-border text-sm">
       <div
@@ -262,7 +292,20 @@ export function Params({ params, onDeclared }: { params: ParamDeclaration[]; onD
         </form>
 
         <div className="min-w-0 flex-1">
-          <div className="mb-1 text-xs text-text-subtle">Declared params</div>
+          <div className="mb-1 flex items-center justify-between gap-2">
+            <span className="text-xs text-text-subtle">Declared params</span>
+            <button
+              type="button"
+              onClick={handleClearAll}
+              disabled={clearing || params.length === 0}
+              className="rounded border border-border-soft px-2 py-0.5 text-xs text-text-secondary hover:bg-surface-2 disabled:opacity-50"
+              title="Clear every declared param, then re-derive params from log lines still held in memory"
+            >
+              {clearing ? 'Clearing…' : 'Clear all'}
+            </button>
+          </div>
+          {clearResult && <div className="mb-1 text-xs text-text-subtle">{clearResult}</div>}
+          {clearError && <div className="mb-1 text-xs text-danger-text">{clearError}</div>}
           <div className="flex flex-wrap gap-1">
             {params.length === 0 && <span className="text-xs text-text-faint">No params declared yet.</span>}
             {params.map((p) => (