fix(ollama): make native num_ctx opt-in

[r266-tech]

Summary

• stop sending native Ollama num_ctx unless it is explicitly configured
• add HINDSIGHT_API_LLM_OLLAMA_NUM_CTX and thread it through config, LLMProvider, and MemoryEngine
• document the migration path for operators who want to keep the old num_ctx=16384 request behavior
• add regression coverage for env parsing, direct-constructor validation, positional timeout compatibility, and native Ollama request options

Fixes #2572.

Tests

• python3 -m py_compile hindsight-api-slim/hindsight_api/config.py hindsight-api-slim/hindsight_api/engine/llm_wrapper.py hindsight-api-slim/hindsight_api/engine/memory_engine.py hindsight-api-slim/hindsight_api/engine/providers/openai_compatible_llm.py hindsight-api-slim/tests/test_config_validation.py hindsight-api-slim/tests/test_llm_wrapper.py
• ruff check hindsight-api-slim/hindsight_api/config.py hindsight-api-slim/hindsight_api/engine/llm_wrapper.py hindsight-api-slim/hindsight_api/engine/memory_engine.py hindsight-api-slim/hindsight_api/engine/providers/openai_compatible_llm.py hindsight-api-slim/tests/test_config_validation.py hindsight-api-slim/tests/test_llm_wrapper.py
• ruff format --check hindsight-api-slim/hindsight_api/config.py hindsight-api-slim/hindsight_api/engine/llm_wrapper.py hindsight-api-slim/hindsight_api/engine/memory_engine.py hindsight-api-slim/hindsight_api/engine/providers/openai_compatible_llm.py hindsight-api-slim/tests/test_config_validation.py hindsight-api-slim/tests/test_llm_wrapper.py

Targeted pytest did not run in this local environment: uv run cannot install onnxruntime==1.27.0 for macOS arm64, and the system Python environment is missing project deps such as asyncpg.

[benfrank241]

really nice bug report and fix — the repro and the ollama ps eviction trace made this trivial to verify. removing the hardcoded num_ctx=16384 and making it opt-in is exactly right, and the validation + regression tests are solid.

i pushed one small commit (da12fd93) adding HINDSIGHT_API_LLM_OLLAMA_NUM_CTX to .env.example (+ the byte-identical hindsight-embed copy) — new config flags need to land there per our checklist, and the env-template sync test stays green. hope you don't mind me pushing directly.

one thing to confirm before i merge: you're threading it from config.llm_ollama_num_ctx rather than per-member/per-bank, so it's static-global. i think that's the right call — context window is a property of the ollama host, not a per-bank preference — but it does diverge from the member.* pattern in that same ensemble block, so just confirm that's intentional and i'll merge.