docs: fix three statements the per-model image strip left stale

The image-rejection recovery no longer switches the session to
text-only or strips history; it records the (provider, model) and
build_api_request strips images from that model's requests only. Three
places still described the old behaviour:

- recover_before_classification docstring and the adjacent comment said
  "switch session to text-only" / "mark session vision-unsupported".
- TestStripImagesDropsStaleApiContent's rationale claimed the strip runs
  on persistent history and that leaving api_content would replay
  rejected images every turn because the recovery gates on
  _image_rejecting_models — false on both counts: current callers pass
  per-call clones. Reworded as the generic helper contract (a rewritten
  persisted row must drop its sidecar) with the no-op note.
- _strip_images_from_messages docstring, same fix.

Comments and docstrings only; no code change.

agent/message_sanitization.py

@@ -337,7 +337,9 @@ def _strip_images_from_messages(messages: list) -> bool:
 
     ``tool`` / ``tool_calls`` messages left empty get a placeholder, NOT deleted (deleting
     orphans the paired ``tool_call_id`` → HTTP 400); other now-empty messages are dropped.
-    Rewritten messages lose their ``api_content`` sidecar (it carries the removed images).
+    Rewritten messages lose their ``api_content`` sidecar (it carries the removed images):
+    a caller rewriting a persisted row must not leave bytes that replay them next turn. The
+    current callers pass per-call clones, where this is a no-op.
     """
     from agent.context_compressor import _DB_PERSISTED_MARKER
     from agent.turn_context import drop_stale_api_content

agent/turn_recovery.py

@@ -236,9 +236,10 @@ def recover_before_classification(
     api_kwargs: Any, active_system_prompt: Any,
 ) -> Tuple[bool, Any]:
     """Recovery branches that run BEFORE ``classify_api_error``: UnicodeEncodeError
-    sanitization, provider image-content rejection (switch session to text-only), and the
-    Bedrock AnthropicBedrock SDK streaming fallback. Returns ``(retry_now,
-    active_system_prompt)``; the prompt may be ASCII-sanitized in place."""
+    sanitization, provider image-content rejection (record the (provider, model);
+    build_api_request strips images from that model's requests only), and the Bedrock
+    AnthropicBedrock SDK streaming fallback. Returns ``(retry_now, active_system_prompt)``;
+    the prompt may be ASCII-sanitized in place."""
     if isinstance(api_error, UnicodeEncodeError) and getattr(agent, '_unicode_sanitization_passes', 0) < 2:
         _recovered, active_system_prompt = _recover_unicode_encode_error(
             agent, api_error, messages, api_messages, api_kwargs, active_system_prompt
@@ -246,8 +247,9 @@ def recover_before_classification(
         if _recovered:
             return True, active_system_prompt
 
-    # Some providers 4xx on image_url content: strip images, mark session
-    # vision-unsupported, retry text-only. English phrase match; extend it.
+    # Some providers 4xx on image_url content: record the (provider, model) and retry;
+    # build_api_request strips images from that model's requests only. English phrase
+    # match; extend it.
     _err_body = ""
     try:
         _err_body = str(getattr(api_error, "body", None) or getattr(api_error, "message", None) or str(api_error))

tests/agent/test_image_rejection_fallback.py

@@ -226,14 +226,14 @@ class TestImageRejectionPhraseIsolation:
 
 
 class TestStripImagesDropsStaleApiContent:
-    """The strip runs on the persistent history, not just the per-call copy.
+    """Generic helper contract: a rewritten row drops its ``api_content`` sidecar.
 
     ``api_content`` is the byte-stability sidecar: it holds the exact bytes
     previously sent for a message, and the next turn substitutes it back into
-    ``content``. Leaving it in place on a message this function rewrote would
-    replay the images the strip just removed — and the recovery cannot re-fire,
-    because it records the model in ``_image_rejecting_models`` and gates itself
-    on that. The session would then send rejected images on every subsequent turn.
+    ``content``. When a caller rewrites a PERSISTED row, the sidecar must go with
+    it or the next turn replays the images the strip just removed. The current
+    callers only pass per-call clones (``api_messages``), where dropping the
+    sidecar is a no-op — the contract is kept for any caller that does not.
 
     Same contract the other content-rewrite paths follow (stale-confirmation
     redaction in ``replay_cleanup``, compression rewrites, merge-into-tail):