feat(plugin): trace follow-ups that join a running turn

A user message sent while the agent is working is absorbed by the run
already in flight — the agent loop re-reads the session's history at the
top of every step, so the message joins the current turn instead of
starting a new one. Laminar had no record of it: `chat.message` returns
early when a turn span is already open, and the turn span's `input` is
serialized once at creation and cannot grow. The only evidence a
follow-up ever arrived was the LLM call's message array getting longer
between one step and the next.

Mark it with a zero-duration `injected_input` span nested in the live
turn, carrying the message parts. It lands between the steps it arrived
between, so the trace shows where in the conversation the follow-up was
picked up, and injections become queryable by span name.

Author: Alezander9

packages/bcode-laminar/VENDOR.md

@@ -40,6 +40,7 @@ worth chasing.
   - OSS users routing bcode telemetry to any OTel collector (Honeycomb, Tempo, Jaeger) without a Laminar account.
   - V4 cloud relaying spans through a backend that holds the real Laminar ingest key — the agent runtime never needs `LMNR_PROJECT_API_KEY`.
   - Default (neither OTel env var set) is unchanged: gRPC to Laminar.
+- **`injected_input` span for follow-ups that join a running turn.** Upstream returns early from `chat.message` when a turn span is already open, so a user message that arrives mid-run is never recorded: the turn span's `input` is serialized once at creation and cannot grow, leaving the LLM call's message array silently getting longer as the only evidence. `startChildSpan` (in `span.ts`) marks it as a zero-duration child of the live turn, carrying the message parts, positioned between the steps it landed between.
 
 ## Behavior preserved
 

packages/bcode-laminar/src/plugin.ts

@@ -17,7 +17,7 @@ import { NodeSDK } from "@opentelemetry/sdk-node"
 
 import { createSpanExporter } from "./exporter"
 import { OpenCodeLaminarSpanProcessor } from "./processor"
-import { startTurnSpan } from "./span"
+import { startChildSpan, startTurnSpan } from "./span"
 import { sessionCurrentTurnSpan, subagentSessionIds } from "./state"
 
 const DEFAULT_GRPC_PORT_LMNR = 8443
@@ -184,7 +184,26 @@ export const LaminarPlugin: Plugin = ({ client }) => {
       const isSubagent = Object.values(subagentSessionIds).some((children) =>
         children.has(sessionID),
       )
-      if (isSubagent || sessionCurrentTurnSpan[sessionID]) return
+      if (isSubagent) return
+
+      // A user message that arrives while a turn is in flight is absorbed by
+      // the run already in progress: the agent loop re-reads the session's
+      // history at the top of every step, so the message joins the turn
+      // instead of starting one. Record it as a point inside the turn — the
+      // turn span's `input` was serialized when the turn opened and cannot
+      // grow, so without this the injected message leaves no trace at all and
+      // the only evidence is the LLM call's message array silently getting
+      // longer.
+      const open = sessionCurrentTurnSpan[sessionID]
+      if (open) {
+        startChildSpan({
+          name: "injected_input",
+          parent: open,
+          sessionId: sessionID,
+          input: { sessionID, messageID, message: output.message, parts: output.parts },
+        }).end()
+        return
+      }
 
       const span = startTurnSpan({
         name: "turn",

packages/bcode-laminar/src/span.ts

@@ -2,8 +2,9 @@
 // lmnr-ts/packages/lmnr/src/laminar.ts. We only need to start a "turn" span
 // per chat.message event with sessionId association, optional parent span
 // context (for callers driving opencode programmatically), and an input
-// payload. No tracing-level, masked-input, global-context-stack, or
-// active-span machinery — opencode owns its own trace lifecycle.
+// payload, plus child spans marking points inside a turn. No tracing-level,
+// masked-input, global-context-stack, or active-span machinery — opencode owns
+// its own trace lifecycle.
 
 import { type Context, ROOT_CONTEXT, type Span, trace, TraceFlags } from "@opentelemetry/api"
 
@@ -56,6 +57,26 @@ export const startTurnSpan = (opts: {
   return trace.getTracer(TURN_TRACER_NAME).startSpan(opts.name, { attributes }, ctx)
 }
 
+// A span nested under one we already hold, for marking a point inside a turn.
+// No parent-path attributes: the processor derives `lmnr.span.path` from the
+// parent's recorded path, which is present because the parent is still open.
+export const startChildSpan = (opts: {
+  name: string
+  parent: Span
+  sessionId: string
+  input?: unknown
+}): Span => {
+  const attributes: Record<string, any> = {
+    [SPAN_TYPE]: "DEFAULT",
+    [SESSION_ID]: opts.sessionId,
+  }
+  if (opts.input !== undefined) attributes[SPAN_INPUT] = JSON.stringify(opts.input)
+
+  return trace
+    .getTracer(TURN_TRACER_NAME)
+    .startSpan(opts.name, { attributes }, trace.setSpan(ROOT_CONTEXT, opts.parent))
+}
+
 type ParsedSpanContext = {
   traceId: string
   spanId: string