diff --git a/CLI/cmux.swift b/CLI/cmux.swift
index 349e16786902..936cd8c25c06 100644
--- a/CLI/cmux.swift
+++ b/CLI/cmux.swift
@@ -25795,7 +25795,7 @@ struct CMUXCLI {
         }
         config["plugin"] = plugins
 
-        let output = try JSONSerialization.data(withJSONObject: config, options: [.prettyPrinted, .sortedKeys])
+        let output = try JSONSerialization.data(withJSONObject: config, options: [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes])
         try output.write(to: shadowJsonURL, options: .atomic)
 
         // Symlink node_modules from the user's config dir so installed packages resolve
@@ -25930,7 +25930,7 @@ struct CMUXCLI {
                attrs[.type] as? FileAttributeType == .typeSymbolicLink {
                 try? fm.removeItem(at: omoConfigURL)
             }
-            let output = try JSONSerialization.data(withJSONObject: omoConfig, options: [.prettyPrinted, .sortedKeys])
+            let output = try JSONSerialization.data(withJSONObject: omoConfig, options: [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes])
             try output.write(to: omoConfigURL, options: .atomic)
         }
 
@@ -33145,7 +33145,7 @@ export default CMUXSessionRestore;
         var plugins = Self.openCodePluginListRemovingSessionPlugin((config["plugin"] as? [Any]) ?? [])
         if shouldInstall, !Self.openCodePluginListContains(plugins, spec: Self.openCodeSessionPluginConfigSpec) { plugins.append(Self.openCodeSessionPluginConfigSpec) }
         config["plugin"] = plugins
-        let output = try JSONSerialization.data(withJSONObject: config, options: [.prettyPrinted, .sortedKeys])
+        let output = try JSONSerialization.data(withJSONObject: config, options: [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes])
         if existingData == output { return false }
         try FileManager.default.createDirectory(at: configDir, withIntermediateDirectories: true)
         try output.write(to: configURL, options: .atomic)
diff --git a/cmuxTests/OpenCodeHookRegressionTests.swift b/cmuxTests/OpenCodeHookRegressionTests.swift
index 95db65577827..8a4a855cd15c 100644
--- a/cmuxTests/OpenCodeHookRegressionTests.swift
+++ b/cmuxTests/OpenCodeHookRegressionTests.swift
@@ -96,6 +96,41 @@ final class OpenCodeHookRegressionTests: XCTestCase {
         XCTAssertEqual(try XCTUnwrap(json["plugin"] as? [String]), ["other-plugin", "./plugins/cmux-session.js"])
     }
 
+    // Regression for https://github.com/manaflow-ai/cmux/issues/7140: opencode resolves
+    // `{file:...}` templates on the raw config text before JSON parsing, so a `\/` written by
+    // slash-escaping serialization turns `{file:./AGENTS.md}` into a bad file reference.
+    func testOpenCodeInstallPreservesFileReferencesWithoutSlashEscaping() throws {
+        let cliPath = try bundledCLIPath()
+        let root = FileManager.default.temporaryDirectory.appendingPathComponent("cmux-opencode-slash-\(UUID().uuidString)", isDirectory: true)
+        let configDir = root.appendingPathComponent("opencode", isDirectory: true)
+        let binDir = root.appendingPathComponent("bin", isDirectory: true)
+        try FileManager.default.createDirectory(at: configDir, withIntermediateDirectories: true)
+        try FileManager.default.createDirectory(at: binDir, withIntermediateDirectories: true)
+        defer { try? FileManager.default.removeItem(at: root) }
+
+        let configURL = configDir.appendingPathComponent("opencode.json", isDirectory: false)
+        try #"{"$schema":"https://opencode.ai/config.json","agent":{"myagent":{"mode":"primary","prompt":"{file:./AGENTS.md}"}},"instructions":["./AGENTS.md"]}"#
+            .write(to: configURL, atomically: true, encoding: .utf8)
+        let fakeOpenCodeURL = binDir.appendingPathComponent("opencode", isDirectory: false)
+        try "#!/bin/sh\nexit 0\n".write(to: fakeOpenCodeURL, atomically: true, encoding: .utf8)
+        chmod(fakeOpenCodeURL.path, 0o755)
+
+        var environment = ProcessInfo.processInfo.environment
+        environment["OPENCODE_CONFIG_DIR"] = configDir.path
+        environment["PATH"] = "\(binDir.path):\(environment["PATH"] ?? "/usr/bin")"
+        environment["CMUX_CLI_SENTRY_DISABLED"] = "1"
+        let result = runProcess(executablePath: cliPath, arguments: ["hooks", "opencode", "install", "--yes"], environment: environment, timeout: 5)
+        XCTAssertFalse(result.timedOut, result.stderr)
+        XCTAssertEqual(result.status, 0, result.stderr)
+
+        // Check the raw bytes: a JSON parser would decode `\/` back to `/` and hide the bug.
+        let rawConfig = try String(contentsOf: configURL, encoding: .utf8)
+        XCTAssertFalse(rawConfig.contains("\\/"), rawConfig)
+        XCTAssertTrue(rawConfig.contains("{file:./AGENTS.md}"), rawConfig)
+        XCTAssertTrue(rawConfig.contains("https://opencode.ai/config.json"), rawConfig)
+        XCTAssertTrue(rawConfig.contains("./plugins/cmux-session.js"), rawConfig)
+    }
+
     func testLegacyHookAliasesAreHiddenFromHelp() throws {
         let cliPath = try bundledCLIPath()
         var environment = ProcessInfo.processInfo.environment
diff --git a/tests/test_cli_omo_openagent_plugin_migration.py b/tests/test_cli_omo_openagent_plugin_migration.py
index ea43d8839185..d7f83519bf48 100644
--- a/tests/test_cli_omo_openagent_plugin_migration.py
+++ b/tests/test_cli_omo_openagent_plugin_migration.py
@@ -58,10 +58,16 @@ def main() -> int:
                     "oh-my-opencode@2.0.0",
                     "oh-my-openagent@3.17.5",
                     ["oh-my-opencode", "1.0.0"],
-                ]
+                ],
+                "instructions": ["{file:./AGENTS.md}"],
             }),
             encoding="utf-8",
         )
+        # No tmux settings, so cmux omo rewrites this config into the shadow dir.
+        (user_config_dir / "oh-my-openagent.json").write_text(
+            json.dumps({"prompt_append": "{file:./AGENTS.md}"}),
+            encoding="utf-8",
+        )
 
         make_executable(
             fake_bin / "opencode",
@@ -104,6 +110,19 @@ def main() -> int:
             print(f"FAIL: invalid shadow opencode.json: {exc}")
             return 1
 
+        # The file references must survive byte for byte: OpenCode does not
+        # resolve an escaped "{file:.\/AGENTS.md}".
+        shadow_omo_json = root / ".cmuxterm" / "omo-config" / "oh-my-openagent.json"
+        for written in (shadow_config_json, shadow_omo_json):
+            try:
+                raw = written.read_text(encoding="utf-8")
+            except Exception as exc:
+                print(f"FAIL: missing {written.name}: {exc}")
+                return 1
+            if "\\/" in raw or '"{file:./AGENTS.md}"' not in raw:
+                print(f"FAIL: {written.name} did not keep the file reference unescaped: {raw!r}")
+                return 1
+
         plugins = shadow_config.get("plugin")
         if not isinstance(plugins, list):
             print(f"FAIL: expected shadow plugin list, got {plugins!r}")