fix(claude_code): parse message-form stream-json + raise on auth-failed (2.0.3)

[CocoRoF]

Summary

Two follow-up bugs from the user's prod run after 2.0.2 unblocked the streaming control flow:

1. output_len=0 despite the pipeline reporting SUCCESS

Claude Code 2.x's default stream-json output emits the full assistant message in one envelope:

{"type":"assistant","message":{"content":[{"type":"text","text":"hi there"}]}}

— not the per-token delta shape ({"type":"assistant","delta":{"type":"text_delta",...}}) the parser was written for. The 2.0.2 accumulator returned an empty APIResponse for every session because its assistant.delta.text_delta branch never matched. User saw:

✓ s06_api
... (5 more stages succeed)
PIPELINE COMPLETE [SUCCESS]: 0 iterations
output_len=0

2. "Not logged in" placeholder came back as the assistant's reply

When the CLI's credential cache is empty it emits a normal-looking assistant frame:

{"type":"assistant","error":"authentication_failed","message":{"content":[{"type":"text","text":"Not logged in · Please run /login"}]}}

The parser accepted it as legitimate output. User got a "successful" turn whose only content was the auth-failure placeholder.

Fix

• StreamJsonAccumulator — one shared parser used by both create_message_stream (streaming caller) and assemble_response_from_stream_json (non-streaming caller). Handles both shapes:
  • delta form (--include-partial-messages on, true streaming)
  • full-message form (Claude Code 2.x default)
  • Synthesises per-block text_delta / thinking_delta / tool_use events when the message form arrives so UI consumers see the same canonical shape they would with true streaming.
• Auth failure: raise APIError(CLI_AUTH_FAILED) when the CLI tags a frame with error="authentication_failed". Host surfaces the auth problem to the user instead of running a successful pipeline that silently returned a placeholder.
• stream_json_line_to_canonical_event (single-event translator) collapses a full message's text blocks into one text_delta for legacy consumers that don't use the accumulator.

Tests

• test_create_message_stream_message_form_collects_text — message form yields text_deltas + populates terminal response
• test_create_message_stream_authentication_failed_raises — auth_failed envelope raises APIError(CLI_AUTH_FAILED)
• test_send_streaming_message_form_text — non-streaming caller picks up message-form text too
• New ok_message_form / message_form_auth_failed scenarios in the fake binary mirror real CLI 2.1.144 output
• Full tests/llm_client/ — 187/187 pass

Release

2.0.3. Migration: none.