diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index e8de64004..a945bb1ac 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -2,12 +2,12 @@
 
 ## [Unreleased]
 
-## [16.0.5] - 2026-06-17
-
 ### Added
 
 - Added `friendlyName` support for hidden secrets so model-visible placeholders can carry sanitized semantic labels, content-derived hashes, and case hints while preserving exact deobfuscation ([#2465](https://github.com/can1357/oh-my-pi/issues/2465)).
 
+## [16.0.5] - 2026-06-17
+
 ### Added
 
 - Added `tui.tight` setting (default `false`) to enable tight layout by removing the 1-character horizontal padding from terminal output.
diff --git a/packages/coding-agent/src/sdk.ts b/packages/coding-agent/src/sdk.ts
index a0e43c27f..057a96c00 100644
--- a/packages/coding-agent/src/sdk.ts
+++ b/packages/coding-agent/src/sdk.ts
@@ -1222,17 +1222,22 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 		const fileEntries = await logger.time("loadSecrets", loadSecrets, cwd, agentDir);
 		const envEntries = collectEnvSecrets();
 		const allEntries = [...envEntries, ...fileEntries];
+		const needsPlaceholderKey = allEntries.some(entry => (entry.mode ?? "obfuscate") === "obfuscate");
+		const placeholderKey = needsPlaceholderKey
+			? await getSecretPlaceholderKey()
+			: await getExistingSecretPlaceholderKey();
 		if (allEntries.length > 0) {
 			// The persisted placeholder key — and creating its key file under the
 			// config root — is only needed for reversible obfuscate-mode placeholders.
 			// Replace-mode entries never build a keyed base, so a replace-only secrets
 			// set must not require the key; otherwise a headless run with an unwritable
 			// config root fails startup for a feature it does not use.
-			const needsPlaceholderKey = allEntries.some(entry => (entry.mode ?? "obfuscate") === "obfuscate");
-			const placeholderKey = needsPlaceholderKey
-				? await getSecretPlaceholderKey()
-				: await getExistingSecretPlaceholderKey();
 			obfuscator = new SecretObfuscator(allEntries, placeholderKey);
+		} else if (placeholderKey !== undefined) {
+			obfuscator = new SecretObfuscator(
+				[{ type: "plain", mode: "replace", content: placeholderKey }],
+				placeholderKey,
+			);
 		}
 	}
 	const secretsEnabled = obfuscator?.hasSecrets() === true;
diff --git a/packages/coding-agent/test/sdk-session-isolation.test.ts b/packages/coding-agent/test/sdk-session-isolation.test.ts
index 1eab2c143..9505b204e 100644
--- a/packages/coding-agent/test/sdk-session-isolation.test.ts
+++ b/packages/coding-agent/test/sdk-session-isolation.test.ts
@@ -170,11 +170,18 @@ describe("createAgentSession session storage isolation", () => {
 				enableLsp: false,
 			};
 
-			const withoutSecrets = await createAgentSession(commonOptions);
+			const existingKeySpy = spyOn(secrets, "getExistingSecretPlaceholderKey").mockImplementation(
+				async () => undefined,
+			);
 			try {
-				expect(withoutSecrets.session.systemPrompt.join("\n")).not.toContain(redactionGuidance);
+				const withoutSecrets = await createAgentSession(commonOptions);
+				try {
+					expect(withoutSecrets.session.systemPrompt.join("\n")).not.toContain(redactionGuidance);
+				} finally {
+					await withoutSecrets.session.dispose();
+				}
 			} finally {
-				await withoutSecrets.session.dispose();
+				existingKeySpy.mockRestore();
 			}
 
 			fs.mkdirSync(path.join(cwd, ".omp"), { recursive: true });
@@ -258,7 +265,7 @@ describe("createAgentSession session storage isolation", () => {
 		});
 	});
 
-	it("requests the placeholder key only when an obfuscate-mode secret is configured", async () => {
+	it("creates the placeholder key only when an obfuscate-mode secret is configured", async () => {
 		await withClearedSecretEnv(async () => {
 			const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), `pi-sdk-secrets-key-${Snowflake.next()}-`));
 			tempDirs.push(tempDir);
@@ -287,6 +294,18 @@ describe("createAgentSession session storage isolation", () => {
 				async () => "existing-placeholder-key",
 			);
 			try {
+				const keyOnly = await createAgentSession(commonOptions);
+				try {
+					expect(keySpy).not.toHaveBeenCalled();
+					expect(existingKeySpy).toHaveBeenCalled();
+					expect(keyOnly.session.obfuscator?.obfuscate("existing-placeholder-key")).not.toContain(
+						"existing-placeholder-key",
+					);
+				} finally {
+					await keyOnly.session.dispose();
+				}
+
+				existingKeySpy.mockClear();
 				// Replace-mode secrets never build a reversible keyed placeholder, so
 				// startup must not create the key file; an existing key is still redacted.
 				fs.writeFileSync(