diff --git a/apps/cli/src/env.ts b/apps/cli/src/env.ts
index 98feb230..822c8e7d 100644
--- a/apps/cli/src/env.ts
+++ b/apps/cli/src/env.ts
@@ -31,6 +31,10 @@ const COMMON_FORWARD_VARS = [
   'SHANNON_AI_MODEL',
   'SHANNON_AI_BASE_URL',
   'SHANNON_AI_OPENAI_FORMAT',
+  // Opt-in debug flag: when set, the worker persists a bounded, sanitized snippet of a failed
+  // provider turn's raw error message to error.log. Off by default; provider prose stays out of
+  // durable state unless an operator deliberately enables it for a diagnosis.
+  'SHANNON_DEBUG_PROVIDER_ERRORS',
   GENERIC_API_KEY_ENV,
 ] as const;
 
diff --git a/apps/worker/src/ai/pi/pi-executor.ts b/apps/worker/src/ai/pi/pi-executor.ts
index ffb9bf5d..7c1f149d 100644
--- a/apps/worker/src/ai/pi/pi-executor.ts
+++ b/apps/worker/src/ai/pi/pi-executor.ts
@@ -49,7 +49,7 @@ import { PI_RETRY_SETTINGS } from './retry-settings.js';
 import { createGlobTool, createTodoWriteTool } from './session-tools.js';
 import { createTaskTool } from './task-tool.js';
 import { TraceEmitter } from './trace-emitter.js';
-import { providerTurnError } from './turn-error.js';
+import { providerTurnError, type SafeProviderTurnDetails, safeProviderTurnDetails } from './turn-error.js';
 
 declare global {
   var SHANNON_DISABLE_LOADER: boolean | undefined;
@@ -163,6 +163,7 @@ async function writeErrorLog(
   duration: number,
   turns: number,
   retryable: boolean,
+  providerDetails?: SafeProviderTurnDetails,
 ): Promise<void> {
   try {
     const errorLog = {
@@ -172,6 +173,7 @@ async function writeErrorLog(
       duration,
       turns,
       retryable,
+      ...(providerDetails !== undefined && { provider: providerDetails }),
     };
     const logPath = path.join(deliverablesDir(sourceDir), 'error.log');
     await fs.appendFile(logPath, `${JSON.stringify(errorLog)}\n`);
@@ -310,6 +312,9 @@ export async function runPiPrompt(
 
   let turnCount = 0;
   let pendingError: PentestError | null = null;
+  // Bounded, non-sensitive facts about the failed turn, captured alongside pendingError so the
+  // error log can distinguish a safeguard/refusal from a transport or tool-call lifecycle fault.
+  let pendingProviderDetails: SafeProviderTurnDetails | null = null;
   // Declared out here so the catch can bill spend accrued before a failure.
   let session: AgentSession | undefined;
 
@@ -359,6 +364,8 @@ export async function runPiPrompt(
           }
           if (msg.role === 'assistant' && msg.stopReason === 'error') {
             pendingError = pendingError ?? providerTurnError(msg, 'Agent error', selection.model.contextWindow);
+            pendingProviderDetails =
+              pendingProviderDetails ?? safeProviderTurnDetails(msg, selection.model.contextWindow);
           }
           break;
         }
@@ -438,7 +445,10 @@ export async function runPiPrompt(
     await traceEmitter?.flush();
     progress.stop();
     outputLines(formatErrorOutput(safeError, execContext, duration, turnCount, retryable));
-    await writeErrorLog(sourceDir, safeError, duration, turnCount, retryable);
+    if (pendingProviderDetails) {
+      console.log(`  provider-turn: ${JSON.stringify(pendingProviderDetails)}`);
+    }
+    await writeErrorLog(sourceDir, safeError, duration, turnCount, retryable, pendingProviderDetails ?? undefined);
 
     // A failed agent still spent money — on its own turns and, since Shannon's
     // prompts delegate the heavy work, mostly on `task` sub-agents. Both count
diff --git a/apps/worker/src/ai/pi/turn-error.ts b/apps/worker/src/ai/pi/turn-error.ts
index 6a17ca29..9415b6a8 100644
--- a/apps/worker/src/ai/pi/turn-error.ts
+++ b/apps/worker/src/ai/pi/turn-error.ts
@@ -6,7 +6,7 @@
 
 import type { AssistantMessage } from '@earendil-works/pi-ai';
 import { classifyProviderFailure, PentestError } from '../../services/error-handling.js';
-import { ErrorCode } from '../../types/errors.js';
+import { ErrorCode, type ProviderFailureCategory } from '../../types/errors.js';
 
 /**
  * Wrap a failed assistant turn, taking the retry verdict from pi.
@@ -33,3 +33,124 @@ export function providerTurnError(message: AssistantMessage, label: string, cont
   error.providerCategory = failure.category;
   return error;
 }
+
+/** One diagnostic entry reduced to bounded, non-prose tokens. */
+interface SafeDiagnostic {
+  readonly type?: string;
+  readonly errorName?: string;
+  readonly errorCode?: string | number;
+}
+
+/**
+ * Bounded, non-sensitive observability facts about a failed assistant turn, safe to persist.
+ *
+ * Carries only closed enums (stop reason, provider category), opaque ids (response id), short
+ * provider/harness tokens (raw stop reason, diagnostic type/name/code), and structural booleans
+ * (redacted thinking, tool call in flight). It never carries the provider's error prose, the
+ * model's generated text, prompts, or credentials. `errorMessage` is reduced to its length, so a
+ * silent empty failure stays distinguishable from one that returned text.
+ */
+export interface SafeProviderTurnDetails {
+  readonly provider?: string;
+  readonly model?: string;
+  readonly responseModel?: string;
+  readonly responseId?: string;
+  readonly stopReason?: string;
+  readonly rawStopReason?: string;
+  readonly endTurn?: boolean;
+  /** True when a thinking block was redacted by the provider's safety filters. */
+  readonly thinkingRedacted: boolean;
+  /** Names of tool calls the model was emitting when the turn errored (own allowlist). */
+  readonly toolCallsInFlight: readonly string[];
+  readonly errorMessageLength: number;
+  /** Present only when SHANNON_DEBUG_PROVIDER_ERRORS is set: a bounded, sanitized error snippet. */
+  readonly errorMessageSnippet?: string;
+  readonly diagnostics?: readonly SafeDiagnostic[];
+  readonly providerCategory: ProviderFailureCategory;
+  readonly retryable: boolean;
+}
+
+/** Whether the operator opted into persisting a bounded snippet of raw provider error text. */
+function debugProviderErrorsEnabled(): boolean {
+  return process.env.SHANNON_DEBUG_PROVIDER_ERRORS === '1' || process.env.SHANNON_DEBUG_PROVIDER_ERRORS === 'true';
+}
+
+/** Collapse whitespace, strip control characters, and truncate. A debug-only view of error prose. */
+function boundedSnippet(value: unknown, max = 500): string | undefined {
+  if (typeof value !== 'string') return undefined;
+  const collapsed = value.replace(/\s+/gu, ' ').trim();
+  return boundedToken(collapsed, max);
+}
+
+/** Strip control characters and truncate, so a provider-controlled token can never carry prose or blobs. */
+function boundedToken(value: unknown, max = 120): string | undefined {
+  if (typeof value !== 'string') return undefined;
+  let out = '';
+  for (let index = 0; index < value.length && out.length < max; index += 1) {
+    const code = value.charCodeAt(index);
+    if (code > 31 && code !== 127) out += value[index];
+  }
+  return out.length > 0 ? out : undefined;
+}
+
+function safeDiagnostics(message: AssistantMessage): SafeDiagnostic[] | undefined {
+  const raw = message.diagnostics;
+  if (!Array.isArray(raw) || raw.length === 0) return undefined;
+  const entries: SafeDiagnostic[] = [];
+  for (const diagnostic of raw.slice(0, 5)) {
+    const type = boundedToken(diagnostic?.type);
+    const errorName = boundedToken(diagnostic?.error?.name);
+    const rawCode = diagnostic?.error?.code;
+    const errorCode = typeof rawCode === 'number' ? rawCode : boundedToken(rawCode, 60);
+    entries.push({
+      ...(type !== undefined && { type }),
+      ...(errorName !== undefined && { errorName }),
+      ...(errorCode !== undefined && { errorCode }),
+    });
+  }
+  return entries;
+}
+
+/**
+ * Extract the bounded observability record from a failed assistant turn. Shares the classifier
+ * with {@link providerTurnError} so the persisted category and retry verdict match the thrown
+ * error exactly.
+ */
+export function safeProviderTurnDetails(message: AssistantMessage, contextWindow?: number): SafeProviderTurnDetails {
+  const failure = classifyProviderFailure(message, contextWindow);
+  const content = Array.isArray(message.content) ? message.content : [];
+  const toolCallsInFlight: string[] = [];
+  for (const block of content) {
+    if (block?.type === 'toolCall') {
+      const name = boundedToken(block.name, 60);
+      if (name !== undefined && toolCallsInFlight.length < 10) toolCallsInFlight.push(name);
+    }
+  }
+  const thinkingRedacted = content.some((block) => block?.type === 'thinking' && block.redacted === true);
+  const diagnostics = safeDiagnostics(message);
+
+  const provider = boundedToken(message.provider);
+  const model = boundedToken(message.model);
+  const responseModel = boundedToken(message.responseModel);
+  const responseId = boundedToken(message.responseId);
+  const stopReason = boundedToken(message.stopReason);
+  const rawStopReason = boundedToken(message.rawStopReason);
+  const errorMessageSnippet = debugProviderErrorsEnabled() ? boundedSnippet(message.errorMessage) : undefined;
+
+  return {
+    ...(provider !== undefined && { provider }),
+    ...(model !== undefined && { model }),
+    ...(responseModel !== undefined && { responseModel }),
+    ...(responseId !== undefined && { responseId }),
+    ...(stopReason !== undefined && { stopReason }),
+    ...(rawStopReason !== undefined && { rawStopReason }),
+    ...(typeof message.endTurn === 'boolean' && { endTurn: message.endTurn }),
+    thinkingRedacted,
+    toolCallsInFlight,
+    errorMessageLength: typeof message.errorMessage === 'string' ? message.errorMessage.length : 0,
+    ...(errorMessageSnippet !== undefined && { errorMessageSnippet }),
+    ...(diagnostics !== undefined && { diagnostics }),
+    providerCategory: failure.category,
+    retryable: failure.retryable,
+  };
+}