fix(FN-2090): log and cover engine warning fallbacks

- Add structured warning logs for plugin-runner fallback paths instead of silent catches
- Add warning telemetry in agent-tools for agent-memory directory, QMD search, and index refresh failures
- Log cron-runner session disposal failures and update agent-logger persistence warnings to use logger output
- Expand engine tests to cover warning behavior across plugin-runner, agent-tools, cron-runner, and agent-logger

packages/engine/src/agent-logger.ts

@@ -6,8 +6,6 @@ const FLUSH_SIZE_BYTES = 1024;
 /** Default timer interval (ms) for periodic flush of small writes. */
 const FLUSH_INTERVAL_MS = 500;
 
-const log = createLogger("agent-logger");
-
 /**
  * Produce a human-readable summary from tool arguments.
  * Returns the full argument value without truncation.
@@ -92,6 +90,7 @@ export class AgentLogger {
   private readonly agent?: AgentRole;
   private readonly externalTextCb?: (taskId: string, delta: string) => void;
   private readonly externalToolCb?: (taskId: string, toolName: string) => void;
+  private readonly log = createLogger("agent-logger");
 
   constructor(options: AgentLoggerOptions) {
     this.store = options.store;
@@ -151,12 +150,7 @@ export class AgentLogger {
     this.flushThinkingBuffer();
     const detail = summarizeToolArgs(name, args);
     this.store.appendAgentLog(this.taskId, name, "tool", detail, this.agent).catch((err) => {
-      log.warn(
-        "Failed to persist tool-start log for task %s (tool: %s): %s",
-        this.taskId,
-        name,
-        err instanceof Error ? err.message : String(err),
-      );
+      this.log.warn(`Failed to log tool start "${name}" for ${this.taskId}: ${err instanceof Error ? err.message : String(err)}`);
     });
   }
 
@@ -176,13 +170,7 @@ export class AgentLogger {
       detail = str.length > 500 ? str.slice(0, 500) + "…" : str;
     }
     this.store.appendAgentLog(this.taskId, name, type, detail, this.agent).catch((err) => {
-      log.warn(
-        "Failed to persist tool-end log for task %s (tool: %s, type: %s): %s",
-        this.taskId,
-        name,
-        type,
-        err instanceof Error ? err.message : String(err),
-      );
+      this.log.warn(`Failed to log tool end "${name}" (${type}) for ${this.taskId}: ${err instanceof Error ? err.message : String(err)}`);
     });
   }
 
@@ -204,11 +192,7 @@ export class AgentLogger {
     const chunk = this.textBuffer;
     this.textBuffer = "";
     return this.store.appendAgentLog(this.taskId, chunk, "text", undefined, this.agent).catch((err) => {
-      log.warn(
-        "Failed to persist text log for task %s: %s",
-        this.taskId,
-        err instanceof Error ? err.message : String(err),
-      );
+      this.log.warn(`Failed to flush text buffer for ${this.taskId}: ${err instanceof Error ? err.message : String(err)}`);
     });
   }
 
@@ -217,11 +201,7 @@ export class AgentLogger {
     const chunk = this.thinkingBuffer;
     this.thinkingBuffer = "";
     return this.store.appendAgentLog(this.taskId, chunk, "thinking", undefined, this.agent).catch((err) => {
-      log.warn(
-        "Failed to persist thinking log for task %s: %s",
-        this.taskId,
-        err instanceof Error ? err.message : String(err),
-      );
+      this.log.warn(`Failed to flush thinking buffer for ${this.taskId}: ${err instanceof Error ? err.message : String(err)}`);
     });
   }