fix(anthropic): coerce blank system text blocks at extraction (#70909) - #86643
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Residual from PR #70910 after #77509 landed the message-list scrub: a whitespace-only system content block carrying a cache_control marker still reached the wire and 400'd the whole request ("text content blocks must contain non-whitespace text"), wedging the session on every retry. The block cannot be dropped (it carries the cache breakpoint), so coerce its text to the shared non-whitespace placeholder when extracting the system param, copying the block so caller message dicts are never mutated. Adds SHL0MS's request-level regression suite from #70910; four of its five cases already pass on main via #77509 — the system-block case fails without this fix.
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૮ >ﻌ< ა ci reviewran on 608febc — fix(anthropic): coerce blank system text blocks at extractio
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This was referenced Aug 15, 2026
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Summary
Salvages the residual fix from #70910 (SHL0MS) after #77509 landed the message-list scrub.
_scrub_blank_text_blocks(fix(anthropic): drop whitespace-only text blocks reaching the Messages API #77509). The remaining leak: a whitespace-only system content block carryingcache_controlis passed through verbatim by the system-extraction path inconvert_messages_to_anthropic, and Anthropic rejects the whole request with HTTP 400 "text content blocks must contain non-whitespace text" — wedging the session on every retry (Session wedges on HTTP 400 'text content blocks must contain non-whitespace text' from a blank block synthesized during request assembly (compression/merge/pre-shaped content) #70909, [Bug]: Session can be poisoned into a permanent non-retryable 400 — whitespace-only user block built at request time #83037)._EMPTY_TEXT_PLACEHOLDER(blocks are copied first, so caller dicts are never mutated; thecache_controlbreakpoint is preserved — it cannot be dropped without losing the cache anchor).tests/agent/test_anthropic_request_blank_block_guard.pyfrom fix(anthropic): prepended leading user turn must be non-whitespace (#70909) #70910 (docstring updated to name the actual backstop on main). Sabotage-verified:test_blank_system_block_is_coercedfails on main without the fix, passes with it.Testing
tests/agent/test_anthropic_request_blank_block_guard.py— 5 passedtests/agent/test_anthropic_whitespace_text_blocks.py+tests/agent/test_anthropic_adapter.py— 110 passedAuthorship preserved: commit authored by SHL0MS. Closes #70909. Supersedes #70910.
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