diff --git a/packages/opencode/src/effect/runner.ts b/packages/opencode/src/effect/runner.ts
index 0e923b1194..1e7d4c2966 100644
--- a/packages/opencode/src/effect/runner.ts
+++ b/packages/opencode/src/effect/runner.ts
@@ -1,10 +1,10 @@
-import { Cause, Deferred, Effect, Exit, Fiber, Schema, Scope, SynchronizedRef } from "effect"
+import { Cause, Deferred, Effect, Exit, Fiber, Latch, Schema, Scope, SynchronizedRef } from "effect"
 
 export interface Runner<A, E = never> {
   readonly state: State<A, E>
   readonly busy: boolean
   readonly ensureRunning: (work: Effect.Effect<A, E>) => Effect.Effect<A, E>
-  readonly startShell: (work: Effect.Effect<A, E>) => Effect.Effect<A, E>
+  readonly startShell: (work: Effect.Effect<A, E>, ready?: Latch.Latch) => Effect.Effect<A, E>
   readonly cancel: Effect.Effect<void>
 }
 
@@ -18,6 +18,8 @@ interface RunHandle<A, E> {
 
 interface ShellHandle<A, E> {
   id: number
+  cancelled: Deferred.Deferred<void>
+  ready?: Latch.Latch
   fiber: Fiber.Fiber<A, E>
 }
 
@@ -59,6 +61,9 @@ export const make = <A, E = never>(
       ? Deferred.fail(done, new Cancelled()).pipe(Effect.asVoid)
       : Deferred.done(done, exit).pipe(Effect.asVoid)
 
+  const awaitDone = (done: Deferred.Deferred<A, E | Cancelled>) =>
+    Deferred.await(done).pipe(Effect.catchTag("RunnerCancelled", (e) => onInterrupt ?? Effect.die(e)))
+
   const idleIfCurrent = () =>
     SynchronizedRef.modify(ref, (st) => [st._tag === "Idle" ? idle : Effect.void, st] as const).pipe(Effect.flatten)
 
@@ -89,7 +94,9 @@ export const make = <A, E = never>(
     SynchronizedRef.modifyEffect(
       ref,
       Effect.fnUntraced(function* (st) {
-        if (st._tag === "Shell" && st.shell.id === id) return [idle, { _tag: "Idle" }] as const
+        if (st._tag === "Shell" && st.shell.id === id) {
+          return [idle, { _tag: "Idle" }] as const
+        }
         if (st._tag === "ShellThenRun" && st.shell.id === id) {
           const run = yield* startRun(st.run.work, st.run.done)
           return [Effect.void, { _tag: "Running", run }] as const
@@ -98,7 +105,12 @@ export const make = <A, E = never>(
       }),
     ).pipe(Effect.flatten)
 
-  const stopShell = (shell: ShellHandle<A, E>) => Fiber.interrupt(shell.fiber)
+  const stopShell = (shell: ShellHandle<A, E>) =>
+    Effect.gen(function* () {
+      if (shell.ready) yield* shell.ready.await.pipe(Effect.exit, Effect.asVoid)
+      yield* Deferred.succeed(shell.cancelled, undefined).pipe(Effect.asVoid)
+      yield* Fiber.interrupt(shell.fiber)
+    })
 
   const ensureRunning = (work: Effect.Effect<A, E>) =>
     SynchronizedRef.modifyEffect(
@@ -107,30 +119,25 @@ export const make = <A, E = never>(
         switch (st._tag) {
           case "Running":
           case "ShellThenRun":
-            return [Deferred.await(st.run.done), st] as const
+            return [awaitDone(st.run.done), st] as const
           case "Shell": {
             const run = {
               id: next(),
               done: yield* Deferred.make<A, E | Cancelled>(),
               work,
             } satisfies PendingHandle<A, E>
-            return [Deferred.await(run.done), { _tag: "ShellThenRun", shell: st.shell, run }] as const
+            return [awaitDone(run.done), { _tag: "ShellThenRun", shell: st.shell, run }] as const
           }
           case "Idle": {
             const done = yield* Deferred.make<A, E | Cancelled>()
             const run = yield* startRun(work, done)
-            return [Deferred.await(done), { _tag: "Running", run }] as const
+            return [awaitDone(done), { _tag: "Running", run }] as const
           }
         }
       }),
-    ).pipe(
-      Effect.flatten,
-      Effect.catch(
-        (e): Effect.Effect<A, E> => (e instanceof Cancelled ? (onInterrupt ?? Effect.die(e)) : Effect.fail(e as E)),
-      ),
-    )
+    ).pipe(Effect.flatten)
 
-  const startShell = (work: Effect.Effect<A, E>) =>
+  const startShell = (work: Effect.Effect<A, E>, ready?: Latch.Latch) =>
     SynchronizedRef.modifyEffect(
       ref,
       Effect.fnUntraced(function* (st) {
@@ -145,13 +152,20 @@ export const make = <A, E = never>(
         }
         yield* busy
         const id = next()
+        const cancelled = yield* Deferred.make<void>()
         const fiber = yield* work.pipe(Effect.ensuring(finishShell(id)), Effect.forkChild)
-        const shell = { id, fiber } satisfies ShellHandle<A, E>
+        const shell = { id, cancelled, ready, fiber } satisfies ShellHandle<A, E>
         return [
           Effect.gen(function* () {
             const exit = yield* Fiber.await(fiber)
             if (Exit.isSuccess(exit)) return exit.value
-            if (Cause.hasInterruptsOnly(exit.cause) && onInterrupt) return yield* onInterrupt
+            if (
+              Cause.hasInterruptsOnly(exit.cause) ||
+              ((yield* Deferred.isDone(cancelled)) && Cause.hasInterrupts(exit.cause) && !Cause.hasDies(exit.cause))
+            ) {
+              if (onInterrupt) return yield* onInterrupt
+              return yield* Effect.die(new Cancelled())
+            }
             return yield* Effect.failCause(exit.cause)
           }),
           { _tag: "Shell", shell },
@@ -183,8 +197,8 @@ export const make = <A, E = never>(
       case "ShellThenRun":
         return [
           Effect.gen(function* () {
-            yield* Deferred.fail(st.run.done, new Cancelled()).pipe(Effect.asVoid)
             yield* stopShell(st.shell)
+            yield* Deferred.fail(st.run.done, new Cancelled()).pipe(Effect.asVoid)
             yield* idleIfCurrent()
           }),
           { _tag: "Idle" } as const,
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index f7306280fe..4c259e4aef 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -45,7 +45,7 @@ import { AppFileSystem } from "@opencode-ai/core/filesystem"
 import { Truncate } from "@/tool/truncate"
 import { decodeDataUrl } from "@/util/data-url"
 import { Process } from "@/util/process"
-import { Cause, Effect, Exit, Layer, Option, Scope, Context, Schema } from "effect"
+import { Cause, Effect, Exit, Latch, Layer, Option, Scope, Context, Schema } from "effect"
 import { zod } from "@/util/effect-zod"
 import { withStatics } from "@/util/schema"
 import * as EffectLogger from "@opencode-ai/core/effect/logger"
@@ -720,143 +720,145 @@ NOTE: At any point in time through this workflow you should feel free to ask the
       } satisfies MessageV2.TextPart)
     })
 
-    const shellImpl = Effect.fn("SessionPrompt.shellImpl")(function* (input: ShellInput) {
-      const ctx = yield* InstanceState.context
-      const run = yield* runner()
-      const session = yield* sessions.get(input.sessionID)
-      if (session.revert) {
-        yield* revert.cleanup(session)
-      }
-      const agent = yield* agents.get(input.agent)
-      if (!agent) {
-        const available = (yield* agents.list()).filter((a) => !a.hidden).map((a) => a.name)
-        const hint = available.length ? ` Available agents: ${available.join(", ")}` : ""
-        const error = new NamedError.Unknown({ message: `Agent not found: "${input.agent}".${hint}` })
-        yield* bus.publish(Session.Event.Error, { sessionID: input.sessionID, error: error.toObject() })
-        throw error
-      }
-      const model = input.model ?? agent.model ?? (yield* lastModel(input.sessionID))
-      const userMsg: MessageV2.User = {
-        id: input.messageID ?? MessageID.ascending(),
-        sessionID: input.sessionID,
-        time: { created: Date.now() },
-        role: "user",
-        agent: input.agent,
-        model: { providerID: model.providerID, modelID: model.modelID },
-      }
-      yield* sessions.updateMessage(userMsg)
-      const userPart: MessageV2.Part = {
-        type: "text",
-        id: PartID.ascending(),
-        messageID: userMsg.id,
-        sessionID: input.sessionID,
-        text: "The following tool was executed by the user",
-        synthetic: true,
-      }
-      yield* sessions.updatePart(userPart)
-
-      const msg: MessageV2.Assistant = {
-        id: MessageID.ascending(),
-        sessionID: input.sessionID,
-        parentID: userMsg.id,
-        mode: input.agent,
-        agent: input.agent,
-        cost: 0,
-        path: { cwd: ctx.directory, root: ctx.worktree },
-        time: { created: Date.now() },
-        role: "assistant",
-        tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
-        modelID: model.modelID,
-        providerID: model.providerID,
-      }
-      yield* sessions.updateMessage(msg)
-      const part: MessageV2.ToolPart = {
-        type: "tool",
-        id: PartID.ascending(),
-        messageID: msg.id,
-        sessionID: input.sessionID,
-        tool: "bash",
-        callID: ulid(),
-        state: {
-          status: "running",
-          time: { start: Date.now() },
-          input: { command: input.command },
-        },
-      }
-      yield* sessions.updatePart(part)
-
-      const cfg = yield* config.get()
-      const sh = Shell.preferred(cfg.shell)
-      const cwd = ctx.directory
-      const args = Shell.args(sh, input.command, cwd)
-      const shellEnv = yield* plugin.trigger(
-        "shell.env",
-        { cwd, sessionID: input.sessionID, callID: part.callID },
-        { env: {} },
-      )
-
-      const cmd = ChildProcess.make(sh, args, {
-        cwd,
-        extendEnv: true,
-        env: { ...shellEnv.env, TERM: "dumb" },
-        stdin: "ignore",
-        forceKillAfter: "3 seconds",
-      })
-
-      let output = ""
-      let aborted = false
-      const finish = Effect.uninterruptible(
+    const shellImpl = Effect.fn("SessionPrompt.shellImpl")(function* (input: ShellInput, ready?: Latch.Latch) {
+      return yield* Effect.uninterruptibleMask((restore) =>
         Effect.gen(function* () {
-          if (aborted) {
-            output += "\n\n" + ["<metadata>", "User aborted the command", "</metadata>"].join("\n")
-          }
-          if (!msg.time.completed) {
-            msg.time.completed = Date.now()
+          const markReady = ready ? ready.open.pipe(Effect.asVoid) : Effect.void
+          const { msg, part, cwd } = yield* Effect.gen(function* () {
+            const ctx = yield* InstanceState.context
+            const session = yield* sessions.get(input.sessionID)
+            if (session.revert) {
+              yield* revert.cleanup(session)
+            }
+            const agent = yield* agents.get(input.agent)
+            if (!agent) {
+              const available = (yield* agents.list()).filter((a) => !a.hidden).map((a) => a.name)
+              const hint = available.length ? ` Available agents: ${available.join(", ")}` : ""
+              const error = new NamedError.Unknown({ message: `Agent not found: "${input.agent}".${hint}` })
+              yield* bus.publish(Session.Event.Error, { sessionID: input.sessionID, error: error.toObject() })
+              throw error
+            }
+            const model = input.model ?? agent.model ?? (yield* lastModel(input.sessionID))
+            const userMsg: MessageV2.User = {
+              id: input.messageID ?? MessageID.ascending(),
+              sessionID: input.sessionID,
+              time: { created: Date.now() },
+              role: "user",
+              agent: input.agent,
+              model: { providerID: model.providerID, modelID: model.modelID },
+            }
+            yield* sessions.updateMessage(userMsg)
+            const userPart: MessageV2.Part = {
+              type: "text",
+              id: PartID.ascending(),
+              messageID: userMsg.id,
+              sessionID: input.sessionID,
+              text: "The following tool was executed by the user",
+              synthetic: true,
+            }
+            yield* sessions.updatePart(userPart)
+
+            const msg: MessageV2.Assistant = {
+              id: MessageID.ascending(),
+              sessionID: input.sessionID,
+              parentID: userMsg.id,
+              mode: input.agent,
+              agent: input.agent,
+              cost: 0,
+              path: { cwd: ctx.directory, root: ctx.worktree },
+              time: { created: Date.now() },
+              role: "assistant",
+              tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
+              modelID: model.modelID,
+              providerID: model.providerID,
+            }
             yield* sessions.updateMessage(msg)
-          }
-          if (part.state.status === "running") {
-            part.state = {
-              status: "completed",
-              time: { ...part.state.time, end: Date.now() },
-              input: part.state.input,
-              title: "",
-              metadata: { output, description: "" },
-              output,
+            const part: MessageV2.ToolPart = {
+              type: "tool",
+              id: PartID.ascending(),
+              messageID: msg.id,
+              sessionID: input.sessionID,
+              tool: "bash",
+              callID: ulid(),
+              state: {
+                status: "running",
+                time: { start: Date.now() },
+                input: { command: input.command },
+              },
             }
             yield* sessions.updatePart(part)
+            return { msg, part, cwd: ctx.directory }
+          }).pipe(Effect.ensuring(markReady))
+
+          const cfg = yield* config.get()
+          const sh = Shell.preferred(cfg.shell)
+          const args = Shell.args(sh, input.command, cwd)
+          let output = ""
+          let aborted = false
+
+          const finish = Effect.uninterruptible(
+            Effect.gen(function* () {
+              if (aborted) {
+                output += "\n\n" + ["<metadata>", "User aborted the command", "</metadata>"].join("\n")
+              }
+              if (!msg.time.completed) {
+                msg.time.completed = Date.now()
+                yield* sessions.updateMessage(msg)
+              }
+              if (part.state.status === "running") {
+                part.state = {
+                  status: "completed",
+                  time: { ...part.state.time, end: Date.now() },
+                  input: part.state.input,
+                  title: "",
+                  metadata: { output, description: "" },
+                  output,
+                }
+                yield* sessions.updatePart(part)
+              }
+            }),
+          )
+
+          const exit = yield* restore(
+            Effect.gen(function* () {
+              const shellEnv = yield* plugin.trigger(
+                "shell.env",
+                { cwd, sessionID: input.sessionID, callID: part.callID },
+                { env: {} },
+              )
+              const cmd = ChildProcess.make(sh, args, {
+                cwd,
+                extendEnv: true,
+                env: { ...shellEnv.env, TERM: "dumb" },
+                stdin: "ignore",
+                forceKillAfter: "3 seconds",
+              })
+              const handle = yield* spawner.spawn(cmd)
+              yield* Stream.runForEach(Stream.decodeText(handle.all), (chunk) =>
+                Effect.gen(function* () {
+                  output += chunk
+                  if (part.state.status === "running") {
+                    part.state.metadata = { output, description: "" }
+                    yield* sessions.updatePart(part)
+                  }
+                }),
+              )
+              yield* handle.exitCode
+            }).pipe(Effect.scoped, Effect.orDie),
+          ).pipe(Effect.exit)
+
+          if (Exit.isFailure(exit) && Cause.hasInterrupts(exit.cause) && !Cause.hasDies(exit.cause)) {
+            aborted = true
           }
+          yield* finish
+
+          if (Exit.isFailure(exit) && !aborted && !Cause.hasInterruptsOnly(exit.cause)) {
+            return yield* Effect.failCause(exit.cause)
+          }
+
+          return { info: msg, parts: [part] }
         }),
       )
-
-      const exit = yield* Effect.gen(function* () {
-        const handle = yield* spawner.spawn(cmd)
-        yield* Stream.runForEach(Stream.decodeText(handle.all), (chunk) =>
-          Effect.sync(() => {
-            output += chunk
-            if (part.state.status === "running") {
-              part.state.metadata = { output, description: "" }
-              void run.fork(sessions.updatePart(part))
-            }
-          }),
-        )
-        yield* handle.exitCode
-      }).pipe(
-        Effect.scoped,
-        Effect.onInterrupt(() =>
-          Effect.sync(() => {
-            aborted = true
-          }),
-        ),
-        Effect.orDie,
-        Effect.ensuring(finish),
-        Effect.exit,
-      )
-
-      if (Exit.isFailure(exit) && !Cause.hasInterruptsOnly(exit.cause)) {
-        return yield* Effect.failCause(exit.cause)
-      }
-
-      return { info: msg, parts: [part] }
     })
 
     const getModel = Effect.fn("SessionPrompt.getModel")(function* (
@@ -1507,7 +1509,8 @@ NOTE: At any point in time through this workflow you should feel free to ask the
 
     const shell: (input: ShellInput) => Effect.Effect<MessageV2.WithParts> = Effect.fn("SessionPrompt.shell")(
       function* (input: ShellInput) {
-        return yield* state.startShell(input.sessionID, lastAssistant(input.sessionID), shellImpl(input))
+        const ready = yield* Latch.make()
+        return yield* state.startShell(input.sessionID, lastAssistant(input.sessionID), shellImpl(input, ready), ready)
       },
     )
 
diff --git a/packages/opencode/src/session/run-state.ts b/packages/opencode/src/session/run-state.ts
index 4b210d63d7..9d4986f174 100644
--- a/packages/opencode/src/session/run-state.ts
+++ b/packages/opencode/src/session/run-state.ts
@@ -1,6 +1,6 @@
 import { InstanceState } from "@/effect/instance-state"
 import { Runner } from "@/effect/runner"
-import { Effect, Layer, Scope, Context } from "effect"
+import { Effect, Latch, Layer, Scope, Context } from "effect"
 import * as Session from "./session"
 import { MessageV2 } from "./message-v2"
 import { SessionID } from "./schema"
@@ -18,6 +18,7 @@ export interface Interface {
     sessionID: SessionID,
     onInterrupt: Effect.Effect<MessageV2.WithParts>,
     work: Effect.Effect<MessageV2.WithParts>,
+    ready?: Latch.Latch,
   ) => Effect.Effect<MessageV2.WithParts>
 }
 
@@ -95,8 +96,9 @@ export const layer = Layer.effect(
       sessionID: SessionID,
       onInterrupt: Effect.Effect<MessageV2.WithParts>,
       work: Effect.Effect<MessageV2.WithParts>,
+      ready?: Latch.Latch,
     ) {
-      return yield* (yield* runner(sessionID, onInterrupt)).startShell(work)
+      return yield* (yield* runner(sessionID, onInterrupt)).startShell(work, ready)
     })
 
     return Service.of({ assertNotBusy, cancel, ensureRunning, startShell })
diff --git a/packages/opencode/test/effect/runner.test.ts b/packages/opencode/test/effect/runner.test.ts
index 4b0fbc1b51..ee99050a8c 100644
--- a/packages/opencode/test/effect/runner.test.ts
+++ b/packages/opencode/test/effect/runner.test.ts
@@ -334,6 +334,22 @@ describe("Runner", () => {
     }),
   )
 
+  it.live(
+    "cancel does not mask shell defects",
+    Effect.gen(function* () {
+      const s = yield* Scope.Scope
+      const runner = Runner.make<string>(s, { onInterrupt: Effect.succeed("interrupted") })
+
+      const sh = yield* runner
+        .startShell(Effect.never.pipe(Effect.ensuring(Effect.die("boom")), Effect.as("ignored")))
+        .pipe(Effect.forkChild)
+      yield* Effect.sleep("10 millis")
+
+      yield* runner.cancel
+      expect(Exit.isFailure(yield* Fiber.await(sh))).toBe(true)
+    }),
+  )
+
   // --- shell→run handoff ---
 
   it.live(
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index 422c1400c9..5330569401 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -1470,6 +1470,10 @@ unix(
 
           const exit = yield* Fiber.await(loop)
           expect(Exit.isSuccess(exit)).toBe(true)
+          if (Exit.isSuccess(exit)) {
+            const tool = completedTool(exit.value.parts)
+            expect(tool?.state.output).toContain("User aborted the command")
+          }
 
           yield* Fiber.await(sh)
         }),