diff --git a/packages/opencode/src/server/server.ts b/packages/opencode/src/server/server.ts
index c33e6deb..bea61a65 100644
--- a/packages/opencode/src/server/server.ts
+++ b/packages/opencode/src/server/server.ts
@@ -59,9 +59,7 @@ const ERRORS = {
     description: "Not found",
     content: {
       "application/json": {
-        schema: resolver(
-          Storage.NotFoundError.Schema
-        )
+        schema: resolver(Storage.NotFoundError.Schema),
       },
     },
   },
@@ -87,12 +85,9 @@ export namespace Server {
         })
         if (err instanceof NamedError) {
           let status: ContentfulStatusCode
-          if (err instanceof Storage.NotFoundError)
-            status = 404
-          else if (err instanceof Provider.ModelNotFoundError)
-            status = 400
-          else
-            status = 500
+          if (err instanceof Storage.NotFoundError) status = 404
+          else if (err instanceof Provider.ModelNotFoundError) status = 400
+          else status = 500
           return c.json(err.toObject(), { status })
         }
         const message = err instanceof Error && err.stack ? err.stack : err.toString()
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index f9c5f363..6ef56a7e 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -1,4 +1,4 @@
-import { streamText, type ModelMessage } from "ai"
+import { streamText, type ModelMessage, LoadAPIKeyError } from "ai"
 import { Session } from "."
 import { Identifier } from "../id/id"
 import { Instance } from "../project/instance"
@@ -13,6 +13,8 @@ import { SessionPrompt } from "./prompt"
 import { Flag } from "../flag/flag"
 import { Token } from "../util/token"
 import { Log } from "../util/log"
+import { SessionLock } from "./lock"
+import { NamedError } from "../util/error"
 
 export namespace SessionCompaction {
   const log = Log.create({ service: "session.compaction" })
@@ -82,7 +84,11 @@ export namespace SessionCompaction {
     }
   }
 
-  export async function run(input: { sessionID: string; providerID: string; modelID: string }) {
+  export async function run(input: { sessionID: string; providerID: string; modelID: string; signal?: AbortSignal }) {
+    if (!input.signal) SessionLock.assertUnlocked(input.sessionID)
+    await using lock = input.signal === undefined ? SessionLock.acquire({ sessionID: input.sessionID }) : undefined
+    const signal = input.signal ?? lock!.signal
+
     await Session.update(input.sessionID, (draft) => {
       draft.time.compacting = Date.now()
     })
@@ -122,6 +128,7 @@ export namespace SessionCompaction {
         created: Date.now(),
       },
     })) as MessageV2.Assistant
+
     const part = (await Session.updatePart({
       type: "text",
       sessionID: input.sessionID,
@@ -133,13 +140,18 @@ export namespace SessionCompaction {
       },
     })) as MessageV2.TextPart
 
-    let summaryText = ""
     const stream = streamText({
       maxRetries: 10,
       model: model.language,
       providerOptions: {
         [model.npm === "@ai-sdk/openai" ? "openai" : model.providerID]: model.info.options,
       },
+      abortSignal: signal,
+      onError(error) {
+        log.error("stream error", {
+          error,
+        })
+      },
       messages: [
         ...system.map(
           (x): ModelMessage => ({
@@ -160,38 +172,88 @@ export namespace SessionCompaction {
       ],
     })
 
-    for await (const value of stream.fullStream) {
-      switch (value.type) {
-        case "text-delta":
-          summaryText += value.text
-          await Session.updatePart({
-            ...part,
-            text: summaryText,
-          })
-          break
-        case "text-end":
-          part.text = summaryText
-          await Session.updatePart({
-            ...part,
-          })
-          break
-        case "finish": {
-          const usage = Session.getUsage({ model: model.info, usage: value.totalUsage, metadata: undefined })
-          msg.cost += usage.cost
-          msg.tokens = usage.tokens
-          msg.summary = true
-          msg.time.completed = Date.now()
-          await Session.updateMessage(msg)
-          part.time!.end = Date.now()
-          await Session.updatePart(part)
-          break
+    try {
+      for await (const value of stream.fullStream) {
+        signal.throwIfAborted()
+        switch (value.type) {
+          case "text-delta":
+            part.text += value.text
+            if (value.providerMetadata) part.metadata = value.providerMetadata
+            if (part.text) await Session.updatePart(part)
+            continue
+          case "text-end": {
+            part.text = part.text.trimEnd()
+            part.time = {
+              start: Date.now(),
+              end: Date.now(),
+            }
+            if (value.providerMetadata) part.metadata = value.providerMetadata
+            await Session.updatePart(part)
+            continue
+          }
+          case "finish-step": {
+            const usage = Session.getUsage({
+              model: model.info,
+              usage: value.usage,
+              metadata: value.providerMetadata,
+            })
+            msg.cost += usage.cost
+            msg.tokens = usage.tokens
+            await Session.updateMessage(msg)
+            continue
+          }
+          case "error":
+            throw value.error
+          default:
+            continue
         }
       }
+    } catch (e) {
+      log.error("compaction error", {
+        error: e,
+      })
+      switch (true) {
+        case e instanceof DOMException && e.name === "AbortError":
+          msg.error = new MessageV2.AbortedError(
+            { message: e.message },
+            {
+              cause: e,
+            },
+          ).toObject()
+          break
+        case MessageV2.OutputLengthError.isInstance(e):
+          msg.error = e
+          break
+        case LoadAPIKeyError.isInstance(e):
+          msg.error = new MessageV2.AuthError(
+            {
+              providerID: model.providerID,
+              message: e.message,
+            },
+            { cause: e },
+          ).toObject()
+          break
+        case e instanceof Error:
+          msg.error = new NamedError.Unknown({ message: e.toString() }, { cause: e }).toObject()
+          break
+        default:
+          msg.error = new NamedError.Unknown({ message: JSON.stringify(e) }, { cause: e })
+      }
+      Bus.publish(Session.Event.Error, {
+        sessionID: input.sessionID,
+        error: msg.error,
+      })
     }
 
-    Bus.publish(Event.Compacted, {
-      sessionID: input.sessionID,
-    })
+    msg.time.completed = Date.now()
+
+    if (!msg.error || MessageV2.AbortedError.isInstance(msg.error)) {
+      msg.summary = true
+      Bus.publish(Event.Compacted, {
+        sessionID: input.sessionID,
+      })
+    }
+    await Session.updateMessage(msg)
 
     return {
       info: msg,
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 29940dda..cced1271 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -211,6 +211,7 @@ export namespace SessionPrompt {
           sessionID: input.sessionID,
           model: model.info,
           providerID: model.providerID,
+          signal: abort.signal,
         }),
         (messages) => insertReminders({ messages, agent }),
       )
@@ -339,7 +340,12 @@ export namespace SessionPrompt {
     }
   }
 
-  async function getMessages(input: { sessionID: string; model: ModelsDev.Model; providerID: string }) {
+  async function getMessages(input: {
+    sessionID: string
+    model: ModelsDev.Model
+    providerID: string
+    signal: AbortSignal
+  }) {
     let msgs = await Session.messages(input.sessionID).then(MessageV2.filterSummarized)
     const lastAssistant = msgs.findLast((msg) => msg.info.role === "assistant")
     if (
@@ -353,6 +359,7 @@ export namespace SessionPrompt {
         sessionID: input.sessionID,
         providerID: input.providerID,
         modelID: input.model.id,
+        signal: input.signal,
       })
       const resumeMsgID = Identifier.ascending("message")
       const resumeMsg = {