feat(logs): coalesce repeated identical lines into one row (×N badge)

A line identical to the last persisted row (level+source+message+path)
within a 5-min refreshing window updates that row — context._repeat counts
the fold, _firstAt keeps the first occurrence, createdAt tracks the latest
so the storm stays at the top of the newest-first viewer. A continuous
storm stays ONE row however long it rages, so it can't evict unrelated
history via the 50k row cap or grind the appliance disk. LogsViewer badges
coalesced rows ×N (tooltip: count + first occurrence, sq/en). In-memory
last-row cache only; a pruned-under-us row falls through to a fresh insert.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/log-service.ts

@@ -25,6 +25,14 @@ const MAX_MESSAGE = 4_000;
 const MAX_STACK = 16_000;
 const MAX_CONTEXT_JSON = 16_000;
 
+/** Storm coalescing: a line identical to the LAST persisted one (level+source+message+
+ *  path) within this window of its previous occurrence UPDATES that row (bumping a
+ *  `_repeat` counter in its context) instead of inserting a new one. A continuous storm
+ *  keeps refreshing the window, so it stays ONE row however long it rages — repeated
+ *  errors can't evict unrelated history or grind the appliance disk (field incident
+ *  2026-07-07: one unreachable controller ≈ hundreds of identical rows/minute). */
+const COALESCE_WINDOW_MS = 300_000;
+
 export interface LogRetention {
   /** Delete logs older than this many days. */
   readonly maxAgeDays: number;
@@ -62,6 +70,16 @@ export class LogService {
   readonly #retention: LogRetention;
   /** Reentrancy guard: never let persisting a log itself emit a persisted log. */
   #writing = false;
+  /** The last persisted row, for storm coalescing (in-memory only; a restart just
+   *  starts a fresh row — best-effort, like everything in this sink). */
+  #last: {
+    id: string;
+    key: string;
+    count: number;
+    firstAt: string;
+    lastAtMs: number;
+    baseContext: Record<string, unknown> | null;
+  } | null = null;
 
   constructor(db: Db, retention: LogRetention = DEFAULT_RETENTION) {
     this.#db = db;
@@ -85,22 +103,53 @@ export class LogService {
     if (this.#writing) return;
     this.#writing = true;
     try {
+      const createdAt = row.createdAt ?? new Date().toISOString();
+      const message = clamp(row.message, MAX_MESSAGE) ?? "";
+      const path = clamp(row.path, 512);
+      const key = `${row.level}|${row.source}|${message}|${path ?? ""}`;
+      const nowMs = Date.now();
+
+      // Storm coalescing: identical to the last persisted row, within the window →
+      // bump that row instead of inserting. createdAt moves to the LATEST occurrence
+      // (keeps the storm visible at the top of the newest-first viewer); the first
+      // occurrence's time is preserved in context._firstAt.
+      const last = this.#last;
+      if (last && last.key === key && nowMs - last.lastAtMs <= COALESCE_WINDOW_MS) {
+        const res = this.#db
+          .update(appLogs)
+          .set({
+            context: { ...(last.baseContext ?? {}), _repeat: last.count + 1, _firstAt: last.firstAt },
+            createdAt,
+          })
+          .where(eq(appLogs.id, last.id))
+          .run();
+        if ((res.changes ?? 0) > 0) {
+          last.count += 1;
+          last.lastAtMs = nowMs;
+          return;
+        }
+        // The row was pruned out from under us — fall through to a fresh insert.
+      }
+
+      const id = randomUUID();
+      const baseContext = safeContext(row.context);
       this.#db
         .insert(appLogs)
         .values({
-          id: randomUUID(),
+          id,
           level: row.level,
           source: row.source,
-          message: clamp(row.message, MAX_MESSAGE) ?? "",
-          context: safeContext(row.context),
+          message,
+          context: baseContext,
           httpStatus: row.httpStatus ?? null,
-          path: clamp(row.path, 512),
+          path,
           stack: clamp(row.stack, MAX_STACK),
           userId: row.userId ?? null,
           userAgent: clamp(row.userAgent, 512),
-          createdAt: row.createdAt ?? new Date().toISOString(),
+          createdAt,
         })
         .run();
+      this.#last = { id, key, count: 1, firstAt: createdAt, lastAtMs: nowMs, baseContext };
     } catch {
       // Swallow — diagnostics must never take down the path they observe. (Can't log
       // it; that's the recursion we're guarding against.)