diff --git a/src/local-agent-claude.test.ts b/src/local-agent-claude.test.ts
index eb1185cc2..b9ff7bf3e 100644
--- a/src/local-agent-claude.test.ts
+++ b/src/local-agent-claude.test.ts
@@ -273,6 +273,13 @@ test("authority settings map each write mode to permissions and sandbox", () =>
   assert.ok((readOnlyPermissions.deny as string[]).includes("Bash"));
   // SAFETY: The surrounding checks or construction already match this type.
   assert.ok((readOnlyPermissions.deny as string[]).includes("Edit"));
+
+  // A nested agent or another file tool must not reopen the writes the parent is denied.
+  for (const tool of ["Write", "MultiEdit", "NotebookEdit", "EnterWorktree", "Agent", "Task", "Workflow", "CronCreate", "RemoteTrigger"]) {
+    // SAFETY: The surrounding checks or construction already match this type.
+    assert.ok((readOnlyPermissions.deny as string[]).includes(tool), tool);
+  }
+
   assert.deepEqual(
     // SAFETY: The surrounding checks or construction already match this type.
     ((readOnlySettings.sandbox as JsonObject).filesystem as JsonObject).allowWrite,
diff --git a/src/local-agent-claude.ts b/src/local-agent-claude.ts
index ac2ae6567..04aae26e2 100644
--- a/src/local-agent-claude.ts
+++ b/src/local-agent-claude.ts
@@ -23,6 +23,24 @@ import type {
 
 type ClaudePermissionMode = "default" | "acceptEdits" | "bypassPermissions" | "plan" | "dontAsk" | "auto";
 
+// Read-only turns deny every tool that writes locally (including EnterWorktree, which creates a Git worktree) and
+// every tool that starts other agents now or later (Agent, Task, Workflow, CronCreate, RemoteTrigger): those agents
+// do not inherit the parent's denies and could do the editing it is refused. The sandbox's denyWrite only covers
+// Bash, not Claude's built-in file tools.
+const CLAUDE_READ_ONLY_DENIED_TOOLS = [
+  "Bash",
+  "Edit",
+  "Write",
+  "MultiEdit",
+  "NotebookEdit",
+  "EnterWorktree",
+  "Agent",
+  "Task",
+  "Workflow",
+  "CronCreate",
+  "RemoteTrigger",
+] as const;
+
 const CLAUDE_WORKSPACE_ALLOWED_TOOLS = [
   // allowedTools is passed as a session/CLI rule, so `/` is anchored to the query cwd.
   "Read(/**)",
@@ -386,7 +404,7 @@ function claudeAuthorityOptions(
 
   const permissions = {
     defaultMode: "dontAsk",
-    deny: allowed ? [] : ["Bash", "Edit"],
+    deny: allowed ? [] : [...CLAUDE_READ_ONLY_DENIED_TOOLS],
   };
 
   const sandbox = {
diff --git a/test/agents-replay/transcripts/claude/read-only.jsonl b/test/agents-replay/transcripts/claude/read-only.jsonl
index 3297f9e6d..1a4544f84 100644
--- a/test/agents-replay/transcripts/claude/read-only.jsonl
+++ b/test/agents-replay/transcripts/claude/read-only.jsonl
@@ -1,6 +1,6 @@
-{"type":"meta","provider":"claude","scenario":"read-only","args":["--output-format","stream-json","--verbose","--input-format","stream-json","--model","haiku","--allowedTools","Read(/**),Edit(/**),Bash","--permission-mode","dontAsk","--settings","{\"permissions\":{\"defaultMode\":\"dontAsk\",\"deny\":[\"Bash\",\"Edit\"]},\"sandbox\":{\"enabled\":true,\"failIfUnavailable\":true,\"autoAllowBashIfSandboxed\":true,\"allowUnsandboxedCommands\":false,\"filesystem\":{\"allowWrite\":[],\"denyWrite\":[\"$WORKSPACE\"]}}}"],"version":"2.1.200 (Claude Code)","recordedAt":"2026-10-26T07:10:31.902Z"}
+{"type":"meta","provider":"claude","scenario":"read-only","args":["--output-format","stream-json","--verbose","--input-format","stream-json","--model","haiku","--allowedTools","Read(/**),Edit(/**),Bash","--permission-mode","dontAsk","--settings","{\"permissions\":{\"defaultMode\":\"dontAsk\",\"deny\":[\"Bash\",\"Edit\",\"Write\",\"MultiEdit\",\"NotebookEdit\",\"EnterWorktree\",\"Agent\",\"Task\",\"Workflow\",\"CronCreate\",\"RemoteTrigger\"]},\"sandbox\":{\"enabled\":true,\"failIfUnavailable\":true,\"autoAllowBashIfSandboxed\":true,\"allowUnsandboxedCommands\":false,\"filesystem\":{\"allowWrite\":[],\"denyWrite\":[\"$WORKSPACE\"]}}}"],"version":"2.1.200 (Claude Code)","recordedAt":"2026-10-26T07:10:31.902Z"}
 {"dir":"in","ms":113,"frame":{"request_id":"5w08fedkj87","type":"control_request","request":{"subtype":"initialize","systemPrompt":[""]}}}
-{"dir":"in","ms":113,"frame":{"request_id":"5v6gd7b4kd6","type":"control_request","request":{"subtype":"apply_flag_settings","settings":{"permissions":{"defaultMode":"dontAsk","deny":["Bash","Edit"]},"sandbox":{"enabled":true,"failIfUnavailable":true,"autoAllowBashIfSandboxed":true,"allowUnsandboxedCommands":false,"filesystem":{"allowWrite":[],"denyWrite":["$WORKSPACE"]}}}}}}
+{"dir":"in","ms":113,"frame":{"request_id":"5v6gd7b4kd6","type":"control_request","request":{"subtype":"apply_flag_settings","settings":{"permissions":{"defaultMode":"dontAsk","deny":["Bash","Edit","Write","MultiEdit","NotebookEdit","EnterWorktree","Agent","Task","Workflow","CronCreate","RemoteTrigger"]},"sandbox":{"enabled":true,"failIfUnavailable":true,"autoAllowBashIfSandboxed":true,"allowUnsandboxedCommands":false,"filesystem":{"allowWrite":[],"denyWrite":["$WORKSPACE"]}}}}}}
 {"dir":"out","ms":1154,"frame":{"type":"control_response","response":{"subtype":"success","request_id":"5w08fedkj87","response":{"commands":[],"agents":[],"output_style":"default","available_output_styles":["default","Proactive","Explanatory","Learning"],"models":[{"value":"default","resolvedModel":"claude-opus-4-8[1m]","displayName":"Default (recommended)","description":"Opus 4.8 with 1M context · Best for everyday, complex tasks","supportsEffort":true,"supportedEffortLevels":["low","medium","high","xhigh","max"],"supportsAdaptiveThinking":true,"supportsFastMode":true,"supportsAutoMode":true},{"value":"opus[1m]","resolvedModel":"claude-opus-4-8[1m]","displayName":"Opus","description":"Opus 4.8 with 1M context · Best for everyday, complex tasks","supportsEffort":true,"supportedEffortLevels":["low","medium","high","xhigh","max"],"supportsAdaptiveThinking":true,"supportsFastMode":true,"supportsAutoMode":true},{"value":"claude-fable-5[1m]","resolvedModel":"claude-fable-5","displayName":"Fable","description":"Fable 5 · Most capable for your hardest and longest-running tasks","supportsEffort":true,"supportedEffortLevels":["low","medium","high","xhigh","max"],"supportsAdaptiveThinking":true,"supportsAutoMode":true},{"value":"sonnet","resolvedModel":"claude-sonnet-5","displayName":"Sonnet","description":"Sonnet 5 · Efficient for routine tasks","supportsEffort":true,"supportedEffortLevels":["low","medium","high","xhigh","max"],"supportsAdaptiveThinking":true,"supportsAutoMode":true},{"value":"haiku","resolvedModel":"claude-haiku-4-5-20251001","displayName":"Haiku","description":"Haiku 4.5 · Fastest for quick answers"}],"account":{},"pid":0,"feedback_survey_config":{"minTimeBeforeFeedbackMs":600000,"minTimeBetweenFeedbackMs":43200000,"minTimeBetweenGlobalFeedbackMs":43200000,"minUserTurnsBeforeFeedback":5,"minUserTurnsBetweenFeedback":25,"hideThanksAfterMs":3000,"onForModels":["*"],"probability":0.05,"lastSurveyShownTime":null}}}}}
 {"dir":"out","ms":1160,"frame":{"type":"control_response","response":{"subtype":"success","request_id":"5v6gd7b4kd6"}}}
 {"dir":"in","ms":1161,"frame":{"request_id":"zpcjtu4elhn","type":"control_request","request":{"subtype":"set_permission_mode","mode":"dontAsk"}}}