diff --git a/packages/core/src/tool/bash.ts b/packages/core/src/tool/bash.ts
index 22423764bc..386755d94a 100644
--- a/packages/core/src/tool/bash.ts
+++ b/packages/core/src/tool/bash.ts
@@ -158,6 +158,8 @@ const layer = Layer.effectDiscard(
               const command = ChildProcess.make(input.command, [], {
                 cwd: target.canonical,
                 shell,
+                env: { OPENCODE: "1", AGENT: "1" },
+                extendEnv: true,
                 stdin: "ignore",
                 detached: process.platform !== "win32",
                 forceKillAfter: Duration.seconds(3),
diff --git a/packages/core/test/tool-bash.test.ts b/packages/core/test/tool-bash.test.ts
index 1e67abe2ba..05e80ca46a 100644
--- a/packages/core/test/tool-bash.test.ts
+++ b/packages/core/test/tool-bash.test.ts
@@ -28,6 +28,8 @@ const runs: Array<{
   readonly command: string
   readonly cwd?: string
   readonly shell?: string | boolean
+  readonly env?: Record<string, string | undefined>
+  readonly extendEnv?: boolean
   readonly options?: AppProcess.RunOptions
 }> = []
 let denyAction: string | undefined
@@ -67,7 +69,14 @@ const appProcess = Layer.succeed(
     run: (command: ChildProcess.Command, options?: AppProcess.RunOptions) =>
       Effect.suspend(() => {
         if (command._tag !== "StandardCommand") throw new Error("expected standard command")
-        runs.push({ command: command.command, cwd: command.options.cwd, shell: command.options.shell, options })
+        runs.push({
+          command: command.command,
+          cwd: command.options.cwd,
+          shell: command.options.shell,
+          env: command.options.env,
+          extendEnv: command.options.extendEnv,
+          options,
+        })
         return runFailure ? Effect.fail(runFailure) : Effect.succeed(result)
       }),
   } as unknown as AppProcess.Interface),
@@ -168,6 +177,7 @@ describe("BashTool", () => {
               },
             })
             expect(runs).toMatchObject([{ command: "pwd", cwd: realpathSync(tmp.path) }])
+            expect(runs[0]).toMatchObject({ env: { OPENCODE: "1", AGENT: "1" }, extendEnv: true })
             expect(runs[0]?.options).toMatchObject({
               combineOutput: true,
               maxOutputBytes: BashTool.MAX_CAPTURE_BYTES,
diff --git a/packages/opencode/src/tool/shell.ts b/packages/opencode/src/tool/shell.ts
index 1e4423e017..e7ef8381c6 100644
--- a/packages/opencode/src/tool/shell.ts
+++ b/packages/opencode/src/tool/shell.ts
@@ -422,6 +422,8 @@ export const ShellTool = Tool.define(
       return {
         ...process.env,
         ...extra.env,
+        OPENCODE: "1",
+        AGENT: "1",
       }
     })
 
diff --git a/packages/opencode/test/tool/shell.test.ts b/packages/opencode/test/tool/shell.test.ts
index a970f85d46..a755aeb769 100644
--- a/packages/opencode/test/tool/shell.test.ts
+++ b/packages/opencode/test/tool/shell.test.ts
@@ -194,6 +194,19 @@ describe("tool.shell", () => {
     ),
   )
 
+  each("identifies commands as running under opencode", () =>
+    runIn(
+      projectRoot,
+      Effect.gen(function* () {
+        const code = "process.stdout.write([process.env.OPENCODE,process.env.AGENT].join(String.fromCharCode(44)))"
+        const command = `${PS.has(sh()) ? "& " : ""}${bin} -e ${evalarg(code)}`
+        const result = yield* run({ command })
+        expect(result.metadata.exit).toBe(0)
+        expect(result.output).toContain("1,1")
+      }),
+    ),
+  )
+
   it.live("falls back from terminal-only configured shell", () =>
     Effect.gen(function* () {
       const tmp = yield* tmpdirScoped({ config: { shell: "fish" } })