Add batch streaming mode: assembly stream --from-stdin

[alexkroman]

Implements batch streaming for the assembly stream command, allowing users to pipe a list of audio file paths or URLs (one per line) to stdin and stream each as its own realtime session in turn.

Summary

This adds the --from-stdin flag to assembly stream, which reads a newline-delimited list of audio sources from stdin and streams each sequentially with its own transcript and LLM chain state. This complements the existing - (raw PCM) stdin mode and enables workflows like ls *.wav | assembly stream --from-stdin.

Key Changes

Core batch streaming logic:

• Added stream_batch_sources() function in aai_cli/streaming/session.py that orchestrates sequential streaming of multiple sources with per-source error handling
• Batch continues on CLIError (file not found, decode failure) but aborts on NotAuthenticated (rejected API key applies to all sources)
• Ctrl-C and broken pipe stop the batch cleanly (exit 0); other failures raise at the end so scripts can trust the exit code

Command integration:

• Added --from-stdin flag to assembly stream command
• Implemented _run_batch() and _collect_batch_sources() in aai_cli/commands/stream/_exec.py to validate flag combinations and collect sources
• Rejects incompatible flags: positional source, --sample, --system-audio, --device, --sample-rate, --show-code
• Deduplicates sources while preserving order (mirrors transcribe --from-stdin behavior)

Streaming session updates:

• Extended StreamSession.run() and _guarded() with handle_interrupt parameter so batch driver owns Ctrl-C/pipe signals across the whole sequence (one Ctrl-C stops the batch, not just the current source)
• Added StreamRenderer.source() method to announce each source in the batch with position (e.g., [2/3] file.wav)

Event and output handling:

• Added Source event type to aai_cli/streaming/events.py for JSON mode segmentation
• JSON mode emits {"type": "source", "source": "...", "index": 1, "total": 2} before each source's events
• Text mode writes source headers to stderr (stdout stays pure transcript lines for piping)
• Human mode prints muted source headers above turns

Validation and error handling:

• Empty stdin raises UsageError with helpful suggestion
• Per-source failures logged as warnings; batch summary at end if any failed
• NotAuthenticated re-raises immediately to abort (one rejected key fails every source)

Testing

Added comprehensive test suite (tests/test_stream_batch.py) covering:

• Sequential streaming in stdin order
• Per-source resolution with sample=False (never coerced to hosted sample)
• Failed source handling (batch continues, exit 1 at end)
• Authentication failure (aborts immediately)
• Ctrl-C and broken pipe lifecycle
• Empty stdin validation

Updated existing tests to include from_stdin=False in defaults and added validation tests for flag conflicts.

Notable Implementation Details

• Batch sources are deduplicated using dict.fromkeys() to preserve order while removing duplicates
• Each source gets a fresh StreamSession from make_session() so transcripts and LLM state don't bleed between sources
• The open_source callback resolves sources with sample=False to ensure real files/URLs are used, never the hosted sample
• Renderer is shared across all sources so JSON output is a continuous NDJSON stream with source events marking boundaries

https://claude.ai/code/session_01AA7v87iZNvfeGKhs2czBqq