Add settings-configurable cap on logs kept in memory (ticket 026)

Settings.max_logs (default None = unlimited) is pushed to the engine
via a new EngineMessage::SetMaxLogs, enforced on every ingest and
whenever the setting changes at runtime (no restart required).
Eviction drops the oldest (lowest-sequence) logs; sequence numbering
isn't renumbered and buckets already derived from an evicted log are
left in place. Exposed via PATCH /api/settings (max_logs: number |
null) and a NavMenu numeric field (blank = unlimited).

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

webapp/src/components/NavMenu.tsx

@@ -1,4 +1,4 @@
-import { useState } from 'react'
+import { useEffect, useState } from 'react'
 import type { Stats } from '../lib/api'
 import type { ColorScheme } from '../lib/api'
 import { useSettingsPanel } from '../lib/useSettingsPanel'
@@ -120,6 +120,25 @@ export function NavMenu({ stats }: { stats: Stats | null }) {
 function SettingsPanel({ panel }: { panel: ReturnType<typeof useSettingsPanel> }) {
   const [filename, setFilename] = useState('')
   const [content, setContent] = useState('')
+  const [maxLogsInput, setMaxLogsInput] = useState('')
+
+  useEffect(() => {
+    setMaxLogsInput(panel.settings?.max_logs != null ? String(panel.settings.max_logs) : '')
+  }, [panel.settings?.max_logs])
+
+  function handleMaxLogsBlur() {
+    const trimmed = maxLogsInput.trim()
+    if (trimmed === '') {
+      panel.setMaxLogs(null)
+      return
+    }
+    const parsed = Number(trimmed)
+    if (!Number.isFinite(parsed) || parsed <= 0) {
+      setMaxLogsInput(panel.settings?.max_logs != null ? String(panel.settings.max_logs) : '')
+      return
+    }
+    panel.setMaxLogs(Math.floor(parsed))
+  }
 
   async function handleFileChange(e: React.ChangeEvent<HTMLInputElement>) {
     const file = e.target.files?.[0]
@@ -158,6 +177,22 @@ function SettingsPanel({ panel }: { panel: ReturnType<typeof useSettingsPanel> }
         </div>
       </section>
 
+      <section>
+        <h3 className="mb-2 text-xs font-semibold uppercase tracking-wide text-text-subtle">Log retention</h3>
+        <div className="flex items-center gap-2">
+          <input
+            type="number"
+            min={1}
+            placeholder="Unlimited"
+            value={maxLogsInput}
+            onChange={(e) => setMaxLogsInput(e.target.value)}
+            onBlur={handleMaxLogsBlur}
+            className="w-28 rounded border border-border-soft bg-surface-1 px-2 py-1 text-xs text-text placeholder:text-text-subtle focus:border-border-strong focus:outline-none"
+          />
+          <span className="text-xs text-text-faint">max logs kept in memory (blank = unlimited)</span>
+        </div>
+      </section>
+
       <section>
         <h3 className="mb-2 text-xs font-semibold uppercase tracking-wide text-text-subtle">Import CSS</h3>
         <form onSubmit={handleImport} className="flex flex-col gap-2">

webapp/src/lib/api.ts

@@ -90,6 +90,8 @@ export type ColorScheme =
 export interface Settings {
   color_scheme: ColorScheme
   active_profile: string | null
+  /** Maximum ingested logs kept in memory; `null` means unlimited. */
+  max_logs: number | null
 }
 
 export type CssEntryKind = 'imported' | 'linked'
@@ -263,8 +265,14 @@ export function fetchSettings(): Promise<Settings> {
   return getJson('/api/settings')
 }
 
-export function updateSettings(update: { colorScheme?: ColorScheme }): Promise<Settings> {
-  return sendJson('/api/settings', 'PATCH', { color_scheme: update.colorScheme })
+export function updateSettings(update: {
+  colorScheme?: ColorScheme
+  /** Omit to leave unchanged; `null` clears the cap back to unlimited. */
+  maxLogs?: number | null
+}): Promise<Settings> {
+  const body: Record<string, unknown> = { color_scheme: update.colorScheme }
+  if ('maxLogs' in update) body.max_logs = update.maxLogs
+  return sendJson('/api/settings', 'PATCH', body)
 }
 
 export function fetchCssEntries(): Promise<CssEntry[]> {

webapp/src/lib/useSettingsPanel.ts

@@ -123,6 +123,15 @@ export function useSettingsPanel() {
     [guarded],
   )
 
+  const setMaxLogs = useCallback(
+    (maxLogs: number | null) =>
+      guarded(async () => {
+        const next = await updateSettings({ maxLogs })
+        setSettings(next)
+      })(),
+    [guarded],
+  )
+
   const importCssEntry = useCallback(
     (filename: string, content: string) =>
       guarded(async () => {
@@ -174,6 +183,7 @@ export function useSettingsPanel() {
     profiles,
     error,
     setColorScheme,
+    setMaxLogs,
     importCssEntry,
     removeCssEntry,
     addProfile,