diff --git a/src/hooks/atlas/tool-execute-before.ts b/src/hooks/atlas/tool-execute-before.ts
index f4e03ad65..d9ede7484 100644
--- a/src/hooks/atlas/tool-execute-before.ts
+++ b/src/hooks/atlas/tool-execute-before.ts
@@ -1,4 +1,5 @@
 import { log } from "../../shared/logger"
+import { replaceToolArgs } from "../../shared/replace-tool-args"
 import { SYSTEM_DIRECTIVE_PREFIX } from "../../shared/system-directive"
 import { isCallerOrchestrator } from "../../shared/session-utils"
 import type { PluginInput } from "@opencode-ai/plugin"
@@ -179,7 +180,7 @@ export function createToolExecuteBeforeHandler(input: {
 
       const prompt = toolOutput.args.prompt as string | undefined
       if (prompt && !prompt.includes(SYSTEM_DIRECTIVE_PREFIX)) {
-        toolOutput.args.prompt = `<system-reminder>${SINGLE_TASK_DIRECTIVE}</system-reminder>\n` + prompt
+        replaceToolArgs(toolOutput, { prompt: `<system-reminder>${SINGLE_TASK_DIRECTIVE}</system-reminder>\n` + prompt })
         log(`[${HOOK_NAME}] Injected single-task directive to task`, {
           sessionID: toolInput.sessionID,
         })
diff --git a/src/plugin/tool-execute-before.ts b/src/plugin/tool-execute-before.ts
index ce1129ccc..508f40dde 100644
--- a/src/plugin/tool-execute-before.ts
+++ b/src/plugin/tool-execute-before.ts
@@ -100,21 +100,20 @@ export function createToolExecuteBeforeHandler(args: {
     }
 
     if (input.tool === "task") {
-      const argsObject = output.args
-      const category = typeof argsObject.category === "string" ? argsObject.category : undefined
-      const subagentType = typeof argsObject.subagent_type === "string" ? argsObject.subagent_type : undefined
-      const taskId = typeof argsObject.task_id === "string" ? argsObject.task_id : undefined
+      const category = typeof output.args.category === "string" ? output.args.category : undefined
+      const subagentType = typeof output.args.subagent_type === "string" ? output.args.subagent_type : undefined
+      const taskId = typeof output.args.task_id === "string" ? output.args.task_id : undefined
 
       if (category) {
-        argsObject.subagent_type = "sisyphus-junior"
+        replaceToolArgs(output, { subagent_type: "sisyphus-junior" })
       } else if (!subagentType && taskId) {
         const resolvedAgent = await resolveSessionAgent(ctx.client, taskId)
-        argsObject.subagent_type = resolvedAgent ?? "continue"
+        replaceToolArgs(output, { subagent_type: resolvedAgent ?? "continue" })
       }
 
       const normalizedSubagentType =
-        typeof argsObject.subagent_type === "string" ? stripInvisibleAgentCharacters(argsObject.subagent_type) : undefined
-      const prompt = typeof argsObject.prompt === "string" ? argsObject.prompt : ""
+        typeof output.args.subagent_type === "string" ? stripInvisibleAgentCharacters(output.args.subagent_type) : undefined
+      const prompt = typeof output.args.prompt === "string" ? output.args.prompt : ""
       const loopState = typeof ctx.directory === "string" ? readState(ctx.directory) : null
       const shouldInjectOracleVerification =
         normalizedSubagentType === "oracle"
@@ -136,12 +135,14 @@ export function createToolExecuteBeforeHandler(args: {
           verification_attempt_id: verificationAttemptId,
           verification_session_id: undefined,
         })
-        argsObject.run_in_background = false
-        argsObject.prompt = buildUltraworkOracleVerificationPrompt(
-          prompt,
-          loopState.prompt,
-          verificationAttemptId,
-        )
+        replaceToolArgs(output, {
+          run_in_background: false,
+          prompt: buildUltraworkOracleVerificationPrompt(
+            prompt,
+            loopState.prompt,
+            verificationAttemptId,
+          ),
+        })
       }
     }
 
diff --git a/src/shared/replace-tool-args.audit.test.ts b/src/shared/replace-tool-args.audit.test.ts
index 4c14faf34..1c85ee6d9 100644
--- a/src/shared/replace-tool-args.audit.test.ts
+++ b/src/shared/replace-tool-args.audit.test.ts
@@ -23,8 +23,10 @@ async function collectTsFiles(dir: string): Promise<string[]> {
 
 const HELPER_FILE = "shared/replace-tool-args.ts"
 
-const DIRECT_MUTATION_PATTERN = /output\.args\.\w+\s*=[^=]/g
-const OBJECT_ASSIGN_PATTERN = /Object\.assign\(\s*output\.args/g
+// Matches direct mutations like `output.args.foo =` or `toolOutput.args.foo =`
+// but excludes comparisons (===, !==, ==)
+const DIRECT_MUTATION_PATTERN = /\w*[Oo]utput\.args\.\w+\s*=[^=]/g
+const OBJECT_ASSIGN_PATTERN = /Object\.assign\(\s*\w*[Oo]utput\.args/g
 
 describe("replace-tool-args audit", () => {
 	it("#given src/**/*.ts files #when scanning for direct output.args mutation #then no matches found outside the helper", async () => {