feat: add OpenAI-compatible Bedrock provider

[skamenan7]

Implements AWS Bedrock inference provider using OpenAI-compatible endpoint for Llama models available through Bedrock.

Closes: #3410

What does this PR do?

Adds AWS Bedrock as an inference provider using the OpenAI-compatible endpoint. This lets us use Bedrock models (GPT-OSS, Llama) through the standard llama-stack inference API.

The implementation uses LiteLLM's OpenAI client under the hood, so it gets all the OpenAI compatibility features. The provider handles per-request API key overrides via headers.

Test Plan

Tested the following scenarios:

• Non-streaming completion - basic request/response flow
• Streaming completion - SSE streaming with chunked responses
• Multi-turn conversations - context retention across turns
• Tool calling - function calling with proper tool_calls format

Bedrock OpenAI-Compatible Provider - Test Results

Model: bedrock-inference/openai.gpt-oss-20b-1:0

---

Test 1: Model Listing

Request:

GET /v1/models HTTP/1.1

Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "data": [
    {"identifier": "bedrock-inference/openai.gpt-oss-20b-1:0", ...},
    {"identifier": "bedrock-inference/openai.gpt-oss-40b-1:0", ...}
  ]
}

---

Test 2: Non-Streaming Completion

Request:

POST /v1/chat/completions HTTP/1.1
Content-Type: application/json

{
  "model": "bedrock-inference/openai.gpt-oss-20b-1:0",
  "messages": [{"role": "user", "content": "Say 'Hello from Bedrock' and nothing else"}],
  "stream": false
}

Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "choices": [{
    "finish_reason": "stop",
    "message": {"content": "...Hello from Bedrock"}
  }],
  "usage": {"prompt_tokens": 79, "completion_tokens": 50, "total_tokens": 129}
}

---

Test 3: Streaming Completion

Request:

POST /v1/chat/completions HTTP/1.1
Content-Type: application/json

{
  "model": "bedrock-inference/openai.gpt-oss-20b-1:0",
  "messages": [{"role": "user", "content": "Count from 1 to 5"}],
  "stream": true
}

Response:

HTTP/1.1 200 OK
Content-Type: text/event-stream

[6 SSE chunks received]
Final content: "1, 2, 3, 4, 5"

---

Test 4: Error Handling - Invalid Model

Request:

POST /v1/chat/completions HTTP/1.1
Content-Type: application/json

{
  "model": "invalid-model-id",
  "messages": [{"role": "user", "content": "Hello"}],
  "stream": false
}

Response:

HTTP/1.1 404 Not Found
Content-Type: application/json

{
  "detail": "Model 'invalid-model-id' not found. Use 'client.models.list()' to list available Models."
}

---

Test 5: Multi-Turn Conversation

Request 1:

POST /v1/chat/completions HTTP/1.1

{
  "messages": [{"role": "user", "content": "My name is Alice"}]
}

Response 1:

HTTP/1.1 200 OK

{
  "choices": [{
    "message": {"content": "...Nice to meet you, Alice! How can I help you today?"}
  }]
}

Request 2 (with history):

POST /v1/chat/completions HTTP/1.1

{
  "messages": [
    {"role": "user", "content": "My name is Alice"},
    {"role": "assistant", "content": "...Nice to meet you, Alice!..."},
    {"role": "user", "content": "What is my name?"}
  ]
}

Response 2:

HTTP/1.1 200 OK

{
  "choices": [{
    "message": {"content": "...Your name is Alice."}
  }],
  "usage": {"prompt_tokens": 183, "completion_tokens": 42}
}

Context retained across turns

---

Test 6: System Messages

Request:

POST /v1/chat/completions HTTP/1.1

{
  "messages": [
    {"role": "system", "content": "You are Shakespeare. Respond only in Shakespearean English."},
    {"role": "user", "content": "Tell me about the weather"}
  ]
}

Response:

HTTP/1.1 200 OK

{
  "choices": [{
    "message": {"content": "Lo! I heed thy request..."}
  }],
  "usage": {"completion_tokens": 813}
}

---

Test 7: Tool Calling

Request:

POST /v1/chat/completions HTTP/1.1

{
  "messages": [{"role": "user", "content": "What's the weather in San Francisco?"}],
  "tools": [{
    "type": "function",
    "function": {
      "name": "get_weather",
      "parameters": {"type": "object", "properties": {"location": {"type": "string"}}}
    }
  }]
}

Response:

HTTP/1.1 200 OK

{
  "choices": [{
    "finish_reason": "tool_calls",
    "message": {
      "tool_calls": [{
        "function": {"name": "get_weather", "arguments": "{\"location\":\"San Francisco\"}"}
      }]
    }
  }]
}

---

Test 8: Sampling Parameters

Request:

POST /v1/chat/completions HTTP/1.1

{
  "messages": [{"role": "user", "content": "Say hello"}],
  "temperature": 0.7,
  "top_p": 0.9
}

Response:

HTTP/1.1 200 OK

{
  "choices": [{
    "message": {"content": "...Hello! 👋 How can I help you today?"}
  }]
}

---

Test 9: Authentication Error Handling

Subtest A: Invalid API Key

Request:

POST /v1/chat/completions HTTP/1.1
x-llamastack-provider-data: {"aws_bedrock_api_key": "invalid-fake-key-12345"}

{"model": "bedrock-inference/openai.gpt-oss-20b-1:0", ...}

Response:

HTTP/1.1 400 Bad Request

{
  "detail": "Invalid value: Authentication failed: Error code: 401 - {'error': {'message': 'Invalid API Key format: Must start with pre-defined prefix', ...}}"
}

---

Subtest B: Empty API Key (Fallback to Config)

Request:

POST /v1/chat/completions HTTP/1.1
x-llamastack-provider-data: {"aws_bedrock_api_key": ""}

{"model": "bedrock-inference/openai.gpt-oss-20b-1:0", ...}

Response:

HTTP/1.1 200 OK

{
  "choices": [{
    "message": {"content": "...Hello! How can I assist you today?"}
  }]
}

Fell back to config key

---

Subtest C: Malformed Token

Request:

POST /v1/chat/completions HTTP/1.1
x-llamastack-provider-data: {"aws_bedrock_api_key": "not-a-valid-bedrock-token-format"}

{"model": "bedrock-inference/openai.gpt-oss-20b-1:0", ...}

Response:

HTTP/1.1 400 Bad Request

{
  "detail": "Invalid value: Authentication failed: Error code: 401 - {'error': {'message': 'Invalid API Key format: Must start with pre-defined prefix', ...}}"
}

[leseb]

Use this one as a reference #3707

[leseb]

Please report the result of the tests/integration/inference/test_openai_completion.py and other openai related tested.

Also why has the uv.lock changed?

[mattf]

• nothing from models.py is used, please remove it
• is the /v1/embeddings endpoint available? if not, add a NotImplementedError stub
• is the /v1/compltions endpoint available? if not...
• great find wrt telemetry and stream usage, after this pr we should consider adding that nugget to the mixin for all providers