Description

Issue Title

[BUG] chunkTimeout does not work for AWS Bedrock and other non-SSE streaming protocols (EventStream)

Issue Body

Summary

The chunkTimeout configuration option in provider.options completely fails to protect AWS Bedrock (and potentially Google Vertex AI) streaming requests. This is due to wrapSSE() in provider.ts checking for text/event-stream content-type, which silently skips all non-SSE protocols like AWS EventStream (application/vnd.amazon.eventstream).

Impact: Bedrock users have no chunk-level timeout protection against silent stream stalls, only the overall timeout (which may be too coarse-grained or disabled).

Reproduction

Environment

• opencode: Installed via npm (~/.nvm/versions/node/v22.22.0/bin/opencode)
• Provider: AWS Bedrock (@ai-sdk/amazon-bedrock)
• Model: global.anthropic.claude-sonnet-4-6

Configuration

~/.config/opencode/opencode.json:

{
  "providers": {
    "my-bedrock": {
      "npm": "@ai-sdk/amazon-bedrock",
      "options": {
        "region": "us-west-2",
        "chunkTimeout": 10,
        "timeout": 60000
      }
    },
    "my-anthropic": {
      "npm": "@ai-sdk/anthropic",
      "options": {
        "apiKey": "sk-ant-...",
        "chunkTimeout": 10,
        "timeout": 60000
      }
    }
  }
}

Test A: AWS Bedrock (10ms chunkTimeout)

Command:

opencode run -m "my-bedrock/global.anthropic.claude-sonnet-4-6" \
  "请写一段300字的文章介绍科技发展"

Expected: Should timeout immediately (actual chunk interval ~50-100ms >> 10ms)

Actual Result:

✅ Request completed successfully
   Full 300-word article generated
   No timeout error

Measured chunk intervals (10 runs, 100-300 word outputs):

• p50: 47ms
• p95: 93ms
• p99: 103ms
• max: 440ms (spike)

All intervals far exceed the 10ms limit, yet no timeout was triggered.

Test B: Standard Anthropic API (10ms chunkTimeout, control group)

Command:

opencode run -m "my-anthropic/claude-sonnet-4-6" \
  "请写一段300字的文章介绍编程语言的发展"

Expected: Should timeout immediately

Actual Result:

❌ Error: SSE read timed out

Conclusion: chunkTimeout works correctly for standard SSE APIs, but completely fails for Bedrock.

Root Cause Analysis

Code Location

packages/opencode/src/provider/provider.ts, line 61-64:

function wrapSSE(res: Response, ms: number, ctl: AbortController) {
  if (typeof ms !== "number" || ms <= 0) return res
  if (!res.body) return res
  
  // ❌ THIS IS THE PROBLEM
  if (!res.headers.get("content-type")?.includes("text/event-stream")) 
    return res  // Bedrock bypasses here, no monitoring installed
  
  // ✅ Only standard SSE reaches this point
  const reader = res.body.getReader()
  const body = new ReadableStream<Uint8Array>({
    async pull(ctrl) {
      const part = await new Promise((resolve, reject) => {
        const id = setTimeout(() => {
          reject(new Error("SSE read timed out"))
        }, ms)
        // ... monitoring logic
      })
      // ...
    }
  })
  return new Response(body, ...)
}

Why Bedrock Bypasses

Bedrock Response Headers (verified):

content-type: application/vnd.amazon.eventstream

The Check:

"application/vnd.amazon.eventstream".includes("text/event-stream")
→ false

Result: wrapSSE returns the raw Response immediately, never installing the chunk timeout monitor.

Why EventStream ≠ SSE

AWS Bedrock uses AWS EventStream (a binary protocol, similar to protobuf), not standard SSE:

• Standard SSE: text/event-stream, text format data: {...}\n\n
• AWS EventStream: application/vnd.amazon.eventstream, binary framing

The AI SDK (@ai-sdk/amazon-bedrock) handles the binary decoding internally, so functionally everything works—except opencode's timeout layer never sees it.

Data Flow Comparison

Standard API (OpenAI, Anthropic direct)

opencode wrapSSE()
  → content-type: text/event-stream ✓
  → Wraps ReadableStream with setTimeout monitoring
  → AI SDK receives monitored stream
  → chunkTimeout works ✅

AWS Bedrock

opencode wrapSSE()
  → content-type: application/vnd.amazon.eventstream ✗
  → Returns raw Response, no monitoring
  → AI SDK decodes EventStream internally
  → Data arrives correctly, but no timeout protection ❌

Affected Scope

Evidence for Vertex AI: Issue #13841 reports identical hanging symptoms with Vertex AI, suggesting it may also use a non-SSE protocol.

Why This Matters

Without chunkTimeout protection:

1. Silent stream stalls (network glitch, model deadlock) go undetected for minutes
2. Only timeout (total duration) can catch it, which is too coarse:
   • A 2-minute task could stall at 1:59 and not be detected for another minute
   • Long tasks (thinking models, large outputs) may disable timeout entirely
3. Users rely on manual intervention (kill -9), as reported in Explore subagent hangs indefinitely with Anthropic Claude Opus 4.6 -- no timeout or recovery #13841, fix(opencode): reconnect on network disruptions (VPN switch, SSE timeout, connection reset) #19116

Measured Bedrock Performance

• Total duration for 300-word output: ~5-6 seconds (normal)
• Total duration for complex reasoning: ~60 seconds (normal)
• Chunk intervals are very stable (p99=103ms), so a 30-second chunkTimeout would catch real stalls without false positives

Proposed Fix

Option A: Remove Content-Type Check (Simplest)

function wrapSSE(res: Response, ms: number, ctl: AbortController) {
  if (typeof ms !== "number" || ms <= 0) return res
  if (!res.body) return res
  
-  if (!res.headers.get("content-type")?.includes("text/event-stream")) 
-    return res
  
  const reader = res.body.getReader()
  // ... existing monitoring logic
}

Rationale: The function monitors raw ReadableStream chunks, which is protocol-agnostic. The AI SDK handles format decoding downstream, so monitoring the byte stream works for all protocols.

Risk: Minimal. Non-streaming responses (JSON) typically don't have res.body and are already filtered by the if (!res.body) return res check.

Option B: Expand Content-Type Match

- if (!res.headers.get("content-type")?.includes("text/event-stream")) 
+ const ct = res.headers.get("content-type") ?? ""
+ if (!ct.includes("text/event-stream") && !ct.includes("eventstream")) 
    return res

Rationale: Explicitly include EventStream variants.

Risk: May catch unintended protocols if any provider uses "eventstream" in a different context.

Option C: Allowlist by Provider

const NEEDS_TIMEOUT = ["@ai-sdk/anthropic", "@ai-sdk/openai", "@ai-sdk/amazon-bedrock", ...]
if (!NEEDS_TIMEOUT.includes(model.api.npm) && !ct.includes("text/event-stream"))
  return res

Risk: High maintenance burden, fragile as new providers are added.

Recommendation

Option A (remove check entirely) is the safest and simplest. The function already has sufficient guards (typeof ms, !res.body), and monitoring the raw byte stream is fundamentally protocol-agnostic.

Related Issues

• Explore subagent hangs indefinitely with Anthropic Claude Opus 4.6 -- no timeout or recovery #13841: Explore subagent hangs indefinitely (Vertex AI, no timeout)
• fix(opencode): reconnect on network disruptions (VPN switch, SSE timeout, connection reset) #19116: Network reconnection fixes (mentions chunk timeout defaults to 30s)
• fix: propagate chunkTimeout to streamText timeout.chunkMs for silent stream dropout detection #25575, fix: propagate chunkTimeout to streamText and add max_retries config #25586: PRs to propagate chunkTimeout to AI SDK (closed due to formatting)

Note: Even if #25575/#25586 were merged (propagating chunkTimeout to AI SDK's streamText), Bedrock would still be broken due to this wrapSSE filter.

Additional Context

This issue was discovered through controlled experiments comparing Bedrock vs. standard API behavior with identical 10ms chunkTimeout settings. Full analysis document available upon request.

System Details:

• OS: macOS (Darwin 24.5.0)
• Node: v22.22.0
• opencode version: Latest from npm
• Test date: 2026-05-09

Plugins

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OpenCode version

1.14.22

Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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