[neilberkman]

The Bedrock OpenAI-family decoder passed provider-supplied role strings to String.to_existing_atom/1. A string without an existing atom raised ArgumentError in the caller's process.

Replace that conversion with explicit mappings for assistant, user, system, and tool. Unknown values fall back to :assistant, matching the default OpenAI-compatible response builder's response role. The default decoder does not use String.to_existing_atom/1 for response roles.

Extend the existing Bedrock OpenAI unit tests to cover all four supported roles, an unknown string, an unsupported string that already has a VM atom (error), and nil. The unknown-string regression failed against the original decoder and passes with the fix.

Audited conversions left unchanged:

• amazon_bedrock/cohere.ex: converts provider-response field names, but rescues ArgumentError and preserves unknown names as strings.
• anthropic.ex: converts caller-supplied tool schema field names during request encoding, and rescues ArgumentError.
• lmstudio.ex: converts caller-supplied reasoning_effort options after an allowlist check; the corresponding atoms are defined in the module.

Verification:

• mix format: passed.
• mix compile --warnings-as-errors: passed.
• mix credo --strict: passed; 625 source files checked, no issues.
• mix test test/req_llm/providers/amazon_bedrock/openai_test.exs: 21 passed.
• mix test: 5,334/5,336 passed, 11 skipped, 240 excluded; two StreamServer synchronization timeouts in metadata_test.exs:147 and error_handling_test.exs:51 (seed 434574).
• mix test --failed: both previously failing tests passed.
• ERL_FLAGS='+S 4:4' mix test --max-cases 4: 5,336 passed, 11 skipped, 240 excluded.

The initial timeout cause was not confirmed. No streaming code was changed. Fixture recording was disabled and no fixtures were modified.

🤖 Generated with Codex and Claude Code

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