feat(llm): halkyon_llm, language models' APIs streamed over plain HTTP (ADR 0021, step 2)

A pure Dart package, no SDKs, one interface (LlmClient) over Anthropic's
Messages API, OpenAI's chat completions, in each known host's dialect and
the local servers' (D45), and OpenAI's Responses API, stateless (D46). A
model's turn keeps what its provider wants back with the tools' results:
Anthropic's thinking blocks, the Responses API's reasoning items and
message phase, Gemini's thought signatures. Failures come by kind, the
provider's words cut and without keys.

Tested on replies written from the providers' documentation, replayed in
pieces of 1, 7 and 4,096 bytes; tool/record_llm.dart records real ones
with a key of one's own, which the tests then run on too (D36).
FakeLlmClient for the code that uses it. BSD-3-Clause, as halkyon_oidc.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_llm/test/fixtures/documented/openai/gemini_status_400.http

@@ -0,0 +1,4 @@
+HTTP 400
+content-type: application/json
+
+[{"error":{"code":400,"message":"Invalid JSON payload received. Unknown name \"store\": Cannot find field.","status":"INVALID_ARGUMENT"}}]

packages/halkyon_llm/test/fixtures/documented/openai/gemini_tool.http

@@ -0,0 +1,9 @@
+HTTP 200
+content-type: text/event-stream
+
+data: {"choices":[{"delta":{"content":"Ich sehe nach.","role":"assistant"},"index":0}],"created":1761400300,"id":"gR0qaZ6uNvqU","model":"gemini-3-flash","object":"chat.completion.chunk","usage":{"completion_tokens":4,"prompt_tokens":472,"total_tokens":540}}
+
+data: {"choices":[{"delta":{"role":"assistant","tool_calls":[{"extra_content":{"google":{"thought_signature":"CiQBcsjafQ=="}},"function":{"arguments":"{\"query\":\"Hund\",\"limit\":5}","name":"find_cards"},"id":"function-call-1","type":"function"}]},"finish_reason":"stop","index":0}],"created":1761400300,"id":"gR0qaZ6uNvqU","model":"gemini-3-flash","object":"chat.completion.chunk","usage":{"completion_tokens":21,"prompt_tokens":472,"total_tokens":561}}
+
+data: [DONE]
+

packages/halkyon_llm/test/fixtures/documented/openai/llamacpp_error.http

@@ -0,0 +1,7 @@
+HTTP 200
+content-type: text/event-stream
+
+data: {"choices":[{"finish_reason":null,"index":0,"delta":{"role":"assistant","content":null}}],"created":1761400500,"id":"chatcmpl-x3Yb","model":"gpt-oss-20b","system_fingerprint":"b6900","object":"chat.completion.chunk"}
+
+data: {"error":{"code":500,"message":"the request exceeds the available context size","type":"server_error"}}
+

packages/halkyon_llm/test/fixtures/documented/openai/mistral_status_422.http

@@ -0,0 +1,4 @@
+HTTP 422
+content-type: application/json
+
+{"object":"error","message":{"detail":[{"type":"extra_forbidden","loc":["body","messages",0,"content"],"msg":"Extra inputs are not permitted","input":"Mein geheimer Text"}]},"type":"invalid_request_message_error","param":null,"code":null}

packages/halkyon_llm/test/fixtures/documented/openai/mistral_tool.http

@@ -0,0 +1,9 @@
+HTTP 200
+content-type: text/event-stream; charset=utf-8
+
+data: {"id":"8c1f0e2a5b7d4c3e9f6a1b2c3d4e5f60","object":"chat.completion.chunk","created":1761400200,"model":"mistral-medium-latest","choices":[{"index":0,"delta":{"role":"assistant","content":""},"finish_reason":null}],"p":"abcdef"}
+
+data: {"id":"8c1f0e2a5b7d4c3e9f6a1b2c3d4e5f60","object":"chat.completion.chunk","created":1761400200,"model":"mistral-medium-latest","choices":[{"index":0,"delta":{"tool_calls":[{"id":"D681PevKs","function":{"name":"find_cards","arguments":"{\"query\": \"Hund\", \"limit\": 5}"},"index":0},{"id":"Qk2Ty7Wb1","function":{"name":"find_cards","arguments":"{\"query\": \"犬\"}"},"index":1}]},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":472,"total_tokens":561,"completion_tokens":89},"p":"ab"}
+
+data: [DONE]
+

packages/halkyon_llm/test/fixtures/documented/openai/ollama_lost_error.http

@@ -0,0 +1,7 @@
+HTTP 200
+content-type: text/event-stream
+
+data: {"id":"chatcmpl-412","object":"chat.completion.chunk","created":1761400400,"model":"qwen3:8b","system_fingerprint":"fp_ollama","choices":[{"index":0,"delta":{"role":"assistant","content":"„Hund“"},"finish_reason":null}]}
+
+data: {"id":"chatcmpl-412","object":"chat.completion.chunk","created":1761400400,"model":"","system_fingerprint":"fp_ollama","choices":[{"index":0,"delta":{"role":"assistant","content":""},"finish_reason":null}]}
+

packages/halkyon_llm/test/fixtures/documented/openai/openrouter_error.http

@@ -0,0 +1,9 @@
+HTTP 200
+content-type: text/event-stream
+
+: OPENROUTER PROCESSING
+
+data: {"id":"gen-1761400600-a","object":"chat.completion.chunk","created":1761400600,"model":"mistralai/mistral-small","provider":"Mistral","choices":[{"index":0,"delta":{"role":"assistant","content":"„Hund“"},"finish_reason":null}]}
+
+data: {"id":"gen-1761400600-a","object":"chat.completion.chunk","created":1761400600,"model":"mistralai/mistral-small","provider":"Mistral","error":{"code":"server_error","message":"Provider disconnected"},"choices":[{"index":0,"delta":{"content":""},"finish_reason":"error"}]}
+

packages/halkyon_llm/test/fixtures/documented/openai/status_400.http

@@ -0,0 +1,4 @@
+HTTP 400
+content-type: application/json
+
+{"error":{"message":"Unsupported parameter: 'max_tokens' is not supported with this model. Use 'max_completion_tokens' instead.","type":"invalid_request_error","param":"max_tokens","code":"unsupported_parameter"}}

packages/halkyon_llm/test/fixtures/documented/openai/status_401.http

@@ -0,0 +1,4 @@
+HTTP 401
+content-type: application/json
+
+{"error":{"message":"Incorrect API key provided: sk-proj-****wxyz. You can find your API key at https://platform.openai.com/account/api-keys.","type":"invalid_request_error","param":null,"code":"invalid_api_key"}}

packages/halkyon_llm/test/fixtures/documented/openai/status_429.http

@@ -0,0 +1,5 @@
+HTTP 429
+content-type: application/json
+retry-after: 20
+
+{"error":{"message":"Rate limit reached for gpt-5-mini in organization org-x on requests per min (RPM): Limit 500, Used 500, Requested 1.","type":"requests","param":null,"code":"rate_limit_exceeded"}}

packages/halkyon_llm/test/fixtures/documented/openai/status_429_quota.http

@@ -0,0 +1,4 @@
+HTTP 429
+content-type: application/json
+
+{"error":{"message":"You exceeded your current quota, please check your plan and billing details.","type":"insufficient_quota","param":null,"code":"insufficient_quota"}}

packages/halkyon_llm/test/fixtures/documented/openai/text.http

@@ -0,0 +1,15 @@
+HTTP 200
+content-type: text/event-stream; charset=utf-8
+
+data: {"id":"chatcmpl-CQ3kT8vLwPz1","object":"chat.completion.chunk","created":1761400000,"model":"gpt-5-mini-2026-08-07","service_tier":"default","system_fingerprint":null,"choices":[{"index":0,"delta":{"role":"assistant","content":"","refusal":null},"logprobs":null,"finish_reason":null}],"usage":null,"obfuscation":"Qx7"}
+
+data: {"id":"chatcmpl-CQ3kT8vLwPz1","object":"chat.completion.chunk","created":1761400000,"model":"gpt-5-mini-2026-08-07","service_tier":"default","system_fingerprint":null,"choices":[{"index":0,"delta":{"content":"„Hund“ heißt auf Japanisch"},"logprobs":null,"finish_reason":null}],"usage":null,"obfuscation":"bR2k9"}
+
+data: {"id":"chatcmpl-CQ3kT8vLwPz1","object":"chat.completion.chunk","created":1761400000,"model":"gpt-5-mini-2026-08-07","service_tier":"default","system_fingerprint":null,"choices":[{"index":0,"delta":{"content":" 犬 (いぬ, inu)."},"logprobs":null,"finish_reason":null}],"usage":null,"obfuscation":"Z"}
+
+data: {"id":"chatcmpl-CQ3kT8vLwPz1","object":"chat.completion.chunk","created":1761400000,"model":"gpt-5-mini-2026-08-07","service_tier":"default","system_fingerprint":null,"choices":[{"index":0,"delta":{},"logprobs":null,"finish_reason":"stop"}],"usage":null,"obfuscation":"m4Tq"}
+
+data: {"id":"chatcmpl-CQ3kT8vLwPz1","object":"chat.completion.chunk","created":1761400000,"model":"gpt-5-mini-2026-08-07","service_tier":"default","system_fingerprint":null,"choices":[],"usage":{"prompt_tokens":412,"completion_tokens":38,"total_tokens":450,"prompt_tokens_details":{"cached_tokens":0,"audio_tokens":0},"completion_tokens_details":{"reasoning_tokens":0,"audio_tokens":0,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"obfuscation":"7y"}
+
+data: [DONE]
+

packages/halkyon_llm/test/fixtures/documented/openai/tool.http

@@ -0,0 +1,19 @@
+HTTP 200
+content-type: text/event-stream; charset=utf-8
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[{"index":0,"delta":{"role":"assistant","content":null,"tool_calls":[{"index":0,"id":"call_DdmO9pD3xa9XTPNJ32zg2hcA","type":"function","function":{"name":"find_cards","arguments":""}}],"refusal":null},"logprobs":null,"finish_reason":null}],"usage":null}
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{\"query\":"}}]},"logprobs":null,"finish_reason":null}],"usage":null}
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"arguments":"\"Hund\",\"limit\":5}"}}]},"logprobs":null,"finish_reason":null}],"usage":null}
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[{"index":0,"delta":{"tool_calls":[{"index":1,"id":"call_7Hq2ZtX0aP4kLm9sB1cD3eF5","type":"function","function":{"name":"find_cards","arguments":""}}]},"logprobs":null,"finish_reason":null}],"usage":null}
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[{"index":0,"delta":{"tool_calls":[{"index":1,"function":{"arguments":"{\"query\":\"犬\"}"}}]},"logprobs":null,"finish_reason":null}],"usage":null}
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[{"index":0,"delta":{},"logprobs":null,"finish_reason":"tool_calls"}],"usage":null}
+
+data: {"id":"chatcmpl-CQ4aB2","object":"chat.completion.chunk","created":1761400100,"model":"gpt-5-mini-2026-08-07","choices":[],"usage":{"prompt_tokens":472,"completion_tokens":89,"total_tokens":561,"prompt_tokens_details":{"cached_tokens":0},"completion_tokens_details":{"reasoning_tokens":64}}}
+
+data: [DONE]
+