fix(bedrock): non-whitespace placeholder for empty Converse text blocks (salvage #66167) - #67978
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Bedrock Converse rejects text content blocks that are empty OR
whitespace-only (ValidationException: "text content blocks must
contain non-whitespace text"). The prior fix attempt substituted a
single space (" ") for missing content -- but a lone space IS
whitespace, so it was rejected by the exact same validation rule it
was meant to satisfy. This caused a deterministic, unrecoverable
retry-loop failure once any blank/whitespace assistant, tool, or user
turn entered history (most commonly via context-compaction rewriting
a turn to a blank string).
Adds _safe_text()/_EMPTY_TEXT_PLACEHOLDER ("(empty)") and applies it
everywhere a blank text block could reach the wire: user/assistant
content conversion, tool results, the assistant-empty-turn fallback,
and the first/last-message user-alternation padding. System-prompt
blocks are the one exception: blank parts are dropped entirely rather
than placeholder-filled, since a system prompt block should never
carry meaningless placeholder text.
Adds tests/agent/test_bedrock_empty_text_blocks.py (11 tests, was
already present uncommitted -- codifies the exact failing history
from issue #9486 and asserts no blank block ever reaches Bedrock).
Verified against the actual failed request dump from this session
(27-message payload) -- replaying it through the fixed converter now
produces zero blank/whitespace-only blocks.
…text, update stale placeholder assertions Addresses hermes-sweeper review on PR #66167: 1. _convert_content_to_converse() still emitted {"text": part} directly for plain-string items inside a content list (as opposed to {"type": "text"} dicts), bypassing _safe_text() entirely. A whitespace-only string item (e.g. [" "]) could still reach Bedrock as a blank block. Now routed through _safe_text(). 2. tests/agent/test_bedrock_adapter.py::TestEmptyTextBlockFix asserted the pre-fix behavior (whitespace -> literal space " "), contradicting the new _safe_text()/_EMPTY_TEXT_PLACEHOLDER behavior added in 4618095. Updated assertions to expect the non-whitespace placeholder, plus added a regression test for the list-string-item case above.
alt-glitch
added
type/bug
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This was referenced Jul 31, 2026
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Summary
Bedrock's Converse path can no longer send whitespace-only text blocks — the API rejects them ("text content blocks must contain non-whitespace text"), and main's lone-space
" "placeholder was itself whitespace, so empty assistant/tool content still 400'd mid-conversation.Salvages the fix half of #66167 (@Polyhistor — both commits cherry-picked with authorship; the PR's context-table half is superseded by the sibling context-lengths PR).
Changes
agent/bedrock_adapter.py:_safe_text()guard routes every content shape (None, empty, whitespace-only, non-string, list items, dict text parts) to a non-whitespace(empty)placeholder in_convert_content_to_conversetests/agent/test_bedrock_empty_text_blocks.py: dedicated 115-line suite; stale lone-space assertions updatedValidation
test_bedrock_adapter.py+test_bedrock_empty_text_blocks.py_convert_content_to_converseCloses #66167 (context-table half superseded; this PR carries the fix half with authorship). Credit: @Polyhistor.
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