diff --git a/apps/desktop/src/shell/DesktopShellEnvironment.test.ts b/apps/desktop/src/shell/DesktopShellEnvironment.test.ts
index 7ec0ab80ae7..8d0bc630ed0 100644
--- a/apps/desktop/src/shell/DesktopShellEnvironment.test.ts
+++ b/apps/desktop/src/shell/DesktopShellEnvironment.test.ts
@@ -45,6 +45,11 @@ function makeProcess(output: string): ChildProcessSpawner.ChildProcessHandle {
   });
 }
 
+function standardCommand(command: ChildProcess.Command): ChildProcess.StandardCommand {
+  assert.equal(command._tag, "StandardCommand");
+  return command as ChildProcess.StandardCommand;
+}
+
 function withProcessEnv<A, E, R>(
   env: NodeJS.ProcessEnv,
   effect: Effect.Effect<A, E, R>,
@@ -173,6 +178,60 @@ describe("DesktopShellEnvironment", () => {
     }),
   );
 
+  it.effect("marks POSIX login shell probes and supplies TERM=dumb when TERM is absent", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+      };
+      const commands: ChildProcess.Command[] = [];
+
+      yield* runShellEnvironment({
+        env,
+        platform: "linux",
+        handler: (command) => {
+          commands.push(command);
+          return envOutput({ PATH: "/usr/local/bin:/usr/bin" });
+        },
+      });
+
+      const command = standardCommand(commands[0] as ChildProcess.Command);
+      assert.deepInclude(command.args, "-ilc");
+      assert.equal(command.options.extendEnv, true);
+      assert.deepEqual(command.options.env, {
+        T3CODE_RESOLVING_ENVIRONMENT: "1",
+        TERM: "dumb",
+      });
+    }),
+  );
+
+  it.effect("preserves inherited TERM for POSIX login shell probes", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        SHELL: "/bin/zsh",
+        PATH: "/usr/bin",
+        TERM: "xterm-256color",
+      };
+      const commands: ChildProcess.Command[] = [];
+
+      yield* runShellEnvironment({
+        env,
+        platform: "darwin",
+        handler: (command) => {
+          commands.push(command);
+          return envOutput({ PATH: "/opt/homebrew/bin:/usr/bin" });
+        },
+      });
+
+      const command = standardCommand(commands[0] as ChildProcess.Command);
+      assert.equal(command.options.extendEnv, true);
+      assert.deepEqual(command.options.env, {
+        T3CODE_RESOLVING_ENVIRONMENT: "1",
+        TERM: "xterm-256color",
+      });
+    }),
+  );
+
   it.effect("falls back to launchctl PATH on macOS when shell probing does not return one", () =>
     Effect.gen(function* () {
       const env: NodeJS.ProcessEnv = {
@@ -243,6 +302,31 @@ describe("DesktopShellEnvironment", () => {
     }),
   );
 
+  it.effect("does not add POSIX probe env to Windows PowerShell probes", () =>
+    Effect.gen(function* () {
+      const env: NodeJS.ProcessEnv = {
+        PATH: "C:\\Windows\\System32",
+      };
+      const commands: ChildProcess.Command[] = [];
+
+      yield* runShellEnvironment({
+        env,
+        platform: "win32",
+        handler: (command) => {
+          commands.push(command);
+          return envOutput({ PATH: "C:\\Windows\\System32" });
+        },
+      });
+
+      assert.isAtLeast(commands.length, 1);
+      for (const command of commands) {
+        const standard = standardCommand(command);
+        assert.isUndefined(standard.options.env);
+        assert.isUndefined(standard.options.extendEnv);
+      }
+    }),
+  );
+
   it.effect("logs command failures with safe probe context and the exact cause", () => {
     const env: NodeJS.ProcessEnv = {
       SHELL: "/bin/bash",
diff --git a/apps/desktop/src/shell/DesktopShellEnvironment.ts b/apps/desktop/src/shell/DesktopShellEnvironment.ts
index 8219f18b7a5..0528c8a92a6 100644
--- a/apps/desktop/src/shell/DesktopShellEnvironment.ts
+++ b/apps/desktop/src/shell/DesktopShellEnvironment.ts
@@ -80,6 +80,7 @@ const WINDOWS_SHELL_CANDIDATES = ["pwsh.exe", "powershell.exe"] as const;
 const LOGIN_SHELL_TIMEOUT = Duration.seconds(5);
 const LAUNCHCTL_TIMEOUT = Duration.seconds(2);
 const PROCESS_TERMINATE_GRACE = Duration.seconds(1);
+const ENVIRONMENT_RESOLUTION_MARKER = "T3CODE_RESOLVING_ENVIRONMENT";
 
 const trimNonEmpty = (value: string | null | undefined): Option.Option<string> =>
   Option.fromNullishOr(value).pipe(
@@ -92,6 +93,13 @@ const pathDelimiter = (platform: NodeJS.Platform) => (platform === "win32" ? ";"
 const readEnvPath = (env: NodeJS.ProcessEnv): Option.Option<string> =>
   trimNonEmpty(env.PATH ?? env.Path ?? env.path);
 
+const loginShellProbeEnv = (
+  env: NodeJS.ProcessEnv,
+): Readonly<Record<string, string | undefined>> => ({
+  [ENVIRONMENT_RESOLUTION_MARKER]: "1",
+  TERM: env.TERM ?? "dumb",
+});
+
 const pathComparisonKey = (entry: string, platform: NodeJS.Platform) => {
   const normalized = entry.trim().replace(/^"+|"+$/g, "");
   return platform === "win32" ? normalized.toLowerCase() : normalized;
@@ -231,11 +239,19 @@ const runCommandOutput = Effect.fn("desktop.shellEnvironment.runCommandOutput")(
   readonly args: ReadonlyArray<string>;
   readonly timeout: Duration.Duration;
   readonly shell?: boolean;
+  readonly env?: Readonly<Record<string, string | undefined>>;
+  readonly extendEnv?: boolean;
 }): Effect.fn.Return<string, never, ChildProcessSpawner.ChildProcessSpawner> {
   const spawner = yield* ChildProcessSpawner.ChildProcessSpawner;
   const output = yield* spawner
     .string(
       ChildProcess.make(input.command, input.args, {
+        ...(input.env === undefined
+          ? {}
+          : {
+              env: input.env,
+              extendEnv: input.extendEnv ?? false,
+            }),
         shell: input.shell ?? false,
         stdin: "ignore",
         stdout: "pipe",
@@ -277,6 +293,7 @@ const runCommandOutput = Effect.fn("desktop.shellEnvironment.runCommandOutput")(
 const readLoginShellEnvironment = (
   shell: string,
   names: ReadonlyArray<string>,
+  env: NodeJS.ProcessEnv,
 ): Effect.Effect<EnvironmentPatch, never, ChildProcessSpawner.ChildProcessSpawner> =>
   names.length === 0
     ? Effect.succeed({})
@@ -284,6 +301,8 @@ const readLoginShellEnvironment = (
         probe: "login-shell",
         command: shell,
         args: ["-ilc", capturePosixEnvironmentCommand(names)],
+        env: loginShellProbeEnv(env),
+        extendEnv: true,
         timeout: LOGIN_SHELL_TIMEOUT,
       }).pipe(Effect.map((output) => extractEnvironment(output, names)));
 
@@ -362,7 +381,7 @@ const installPosixEnvironment = Effect.fn("desktop.shellEnvironment.installPosix
     for (const shell of listLoginShellCandidates(config)) {
       Object.assign(
         shellEnvironment,
-        yield* readLoginShellEnvironment(shell, LOGIN_SHELL_ENV_NAMES),
+        yield* readLoginShellEnvironment(shell, LOGIN_SHELL_ENV_NAMES, config.env),
       );
       if (shellEnvironment.PATH) break;
     }