diff --git a/README.md b/README.md
index f27266d..f8906dd 100644
--- a/README.md
+++ b/README.md
@@ -173,7 +173,7 @@ client.receive().takeWhile { env ->
     when (val p = env.payload) {
         is JobStatusEvent  -> { println("status: ${p.phase} ${p.body}"); true }
         is JobProgress     -> { println("progress: ${p.percent}% ${p.message}"); true }
-        is Metric          -> { println("metric: ${p.name}=${p.value} ${p.unit ?: ""}"); true }
+        is Metric          -> { println("metric: ${p.name}=${p.value} ${p.unit}"); true }
         is JobResultChunk  -> { chunks.accept(p); true }
         is JobCompleted    -> { println("result: ${p.result}"); false }
         is JobFailed       -> { println("failed: ${p.code} ${p.message}"); false }
@@ -222,7 +222,7 @@ try {
     client.receive().collect { env ->
         val m = env.payload as? Metric ?: return@collect
         if (m.name == StandardMetrics.COST_BUDGET_REMAINING) {
-            println("budget remaining: ${m.value} ${m.unit ?: ""}")
+            println("budget remaining: ${m.value} ${m.unit}")
         }
     }
 } catch (e: ARCPException.BudgetExhausted) {
diff --git a/docs/guides/job-events.md b/docs/guides/job-events.md
index cc44b55..c3d3a2b 100644
--- a/docs/guides/job-events.md
+++ b/docs/guides/job-events.md
@@ -8,7 +8,7 @@ progress, heartbeat, chunk, and status events.
 Sent when the agent begins executing:
 
 ```kotlin
-is JobStarted -> println("Job ${msg.jobId} is now running")
+is JobStarted -> println("Job ${env.jobId} is now running")
 ```
 
 ## JobProgress
diff --git a/lib/src/main/kotlin/dev/arcp/client/ResultChunkAssembler.kt b/lib/src/main/kotlin/dev/arcp/client/ResultChunkAssembler.kt
index dbfefbb..ebc3a09 100644
--- a/lib/src/main/kotlin/dev/arcp/client/ResultChunkAssembler.kt
+++ b/lib/src/main/kotlin/dev/arcp/client/ResultChunkAssembler.kt
@@ -6,7 +6,12 @@ import dev.arcp.messages.ResultChunkEncoding
 import kotlin.io.encoding.Base64
 import kotlin.io.encoding.ExperimentalEncodingApi
 
-/** Client-side accumulator for `result_chunk` streams (RFC v1.1 §8.4). */
+/**
+ * Client-side accumulator for `result_chunk` streams (RFC v1.1 §8.4).
+ *
+ * Not thread-safe: use one assembler per result stream and call [accept]
+ * from a single coroutine.
+ */
 public class ResultChunkAssembler(
     private val maxAssembledSize: Long = DEFAULT_MAX_ASSEMBLED_SIZE,
 ) {
diff --git a/lib/src/main/kotlin/dev/arcp/messages/Session.kt b/lib/src/main/kotlin/dev/arcp/messages/Session.kt
index d0b12e0..b91ac99 100644
--- a/lib/src/main/kotlin/dev/arcp/messages/Session.kt
+++ b/lib/src/main/kotlin/dev/arcp/messages/Session.kt
@@ -25,7 +25,8 @@ public enum class HeartbeatRecovery {
 /**
  * Negotiated capability set (RFC §7).
  *
- * Absent boolean fields default to `false` per §7. The `extensions` list
+ * Absent boolean fields default to `false` per §7, except `interrupt`,
+ * which defaults to `true` for SDK ergonomics. The `extensions` list
  * advertises the namespaces accepted on this session (RFC §21.2).
  */
 @Serializable
@@ -47,6 +48,7 @@ public data class Capabilities(
     @SerialName("model.use")
     val modelUse: Boolean = false,
     val anonymous: Boolean = false,
+    /** Deliberately defaults to `true` for pause-and-ask ergonomics. */
     val interrupt: Boolean = true,
     @SerialName("heartbeat_interval_seconds")
     val heartbeatIntervalSeconds: Int = DEFAULT_HEARTBEAT_INTERVAL_SECONDS,
diff --git a/lib/src/test/kotlin/dev/arcp/runtime/CapabilityNegotiationTest.kt b/lib/src/test/kotlin/dev/arcp/runtime/CapabilityNegotiationTest.kt
new file mode 100644
index 0000000..ddea4ec
--- /dev/null
+++ b/lib/src/test/kotlin/dev/arcp/runtime/CapabilityNegotiationTest.kt
@@ -0,0 +1,17 @@
+package dev.arcp.runtime
+
+import dev.arcp.messages.Capabilities
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class CapabilityNegotiationTest :
+    StringSpec({
+        "interrupt stays enabled when both peers use defaults" {
+            val proposed = Capabilities()
+            val supported = Capabilities()
+
+            val result = negotiate(proposed, supported)
+
+            result.negotiated.interrupt shouldBe true
+        }
+    })