drb-correlation-review on the prior commit flagged two ways the per-scene
transcript could silently fall back to the whole-call text:
1. _build_transcript_block numbered transmissions "1." while the prompt says
"0-based indices" — a model echoing the labels it saw returned 1-based
indices, shifting every scene's slice by one. Labels are now "0." to match
the documented contract (also fixes the same latent skew in
_build_scene_embed_text / #80).
2. An empty join (bad / out-of-range / non-int indices) hit
`transcript or call_doc.get(...)` in _build_context and fell back to the
whole-call transcript — re-opening the leak exactly when indices are wrong.
The slice now falls back to this call's own whole transcript *before*
_build_context sees it, so it is never "". Non-int and negative indices
are rejected rather than raising.
Slice logic extracted to `_scene_transcript_text` with a dedicated test file
(4 cases: subset, corrected-wins, no-indices fallback, bad-indices fallback).
Call-doc fallback kept (sweep / no-scene path) per the review. Also restored
the `-> ` spacing lost in the prior commit's kwarg edit.
Full c2-core suite green: 300 passed (sandboxed venv). Still DO NOT MERGE
until the measurement window closes.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
