fix(laminar): drain OTel processors before process.exit() to stop losing final agent spans

Eval traces were missing the final LLM span on ~27% of runs (gemini-3-flash
76%, glm-5.1 34%, mimo 14%, gpt-5.5 1%, claude 0%). Root cause is a
process-exit race: the plugin event hook in packages/opencode/src/plugin/index.ts:249
is invoked fire-and-forget (`void hook["event"]?.(...)`), so the bcode-laminar
`session.idle` handler's `processor.forceFlush()` Promise is discarded, and
the unconditional `process.exit()` in the top-level `finally` (index.ts:252)
kills in-flight gRPC exports.

Model-dependence comes from emit shape: tool-only-then-final-text models
(glm-5.1, gemini-3-flash) make one extra tool-less LLM round at the end whose
lone `ai.streamText.doStream` span ends 50-200ms before idle and is the
freshest unflushed thing in the BatchSpanProcessor queue at exit. Tool-call+
text-in-same-step models (claude-opus, gpt-5.5) fold the final answer into a
step that ended seconds earlier and was already flushed in a prior batch.

Fix: in the top-level `finally` of index.ts, before `process.exit()`, fetch
the global OTel TracerProvider via `@opentelemetry/api`, duck-check
`forceFlush`, and race it against a 3 s timeout so a wedged exporter cannot
hang bcode on exit. Generic to any OTel-based plugin.

Does not touch the deeper bug (the fire-and-forget `event` hook); that is
the proper upstream fix to anomalyco/opencode.

Author: bcode

packages/opencode/src/index.ts

@@ -45,6 +45,7 @@ import { PluginCommand } from "./cli/cmd/plug"
 import { Heap } from "./cli/heap"
 import { drizzle } from "drizzle-orm/bun-sqlite"
 import { ensureProcessMetadata } from "@opencode-ai/core/util/opencode-process"
+import { trace } from "@opentelemetry/api"
 
 const processMetadata = ensureProcessMetadata("main")
 
@@ -245,6 +246,20 @@ try {
   }
   process.exitCode = 1
 } finally {
+  // Drain any registered OTel span processors (e.g. bcode-laminar) before
+  // exiting. The plugin's `session.idle` event handler is invoked
+  // fire-and-forget (`packages/opencode/src/plugin/index.ts:249`), so its
+  // `processor.forceFlush()` Promise was never awaited — without this drain,
+  // `process.exit()` kills any in-flight gRPC export and the final agent
+  // span is lost. Bounded with a 3 s race so a wedged exporter cannot hang
+  // bcode on exit. Generic to any OTel-based plugin, not laminar-specific.
+  const provider = trace.getTracerProvider() as { forceFlush?: () => Promise<void> }
+  if (provider.forceFlush) {
+    await Promise.race([
+      provider.forceFlush().catch(() => {}),
+      new Promise<void>((resolve) => setTimeout(resolve, 3000)),
+    ])
+  }
   // Some subprocesses don't react properly to SIGTERM and similar signals.
   // Most notably, some docker-container-based MCP servers don't handle such signals unless
   // run using `docker run --init`.