fix(sse): hoist leading text system messages on the Claude mid-conversation-system passthrough (Anthropic 400) - #13072
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diegosouzapw merged 1 commit intoSep 9, 2026
Conversation
…sation-system passthrough
On the Claude Code semantic passthrough with a 1M-context model (system + tools
present), system-role messages are deliberately kept inside messages[] and only
directive-only messages (content: [] + output_config) are relocated off
messages[0]. Anthropic also rejects a text-bearing system message at messages[0]:
messages.0: use the top-level 'system' parameter for the initial system
prompt; the directive-only form (content: [] with output_config) is
accepted at any position
That is exactly where the Output Styles injection lands
(open-sse/services/compression/outputStyles/apply.ts unshifts a system message),
so every Claude Code turn with an output style active on such a model fails
with 400.
Add hoistLeadingTextSystemMessages(): move only the leading run of text-bearing
system-role messages (everything before the first user/assistant turn) into the
top-level system parameter, and call it before relocateDirectiveOnlyMessages()
on that path. Genuine mid-conversation system turns keep their position and
cache prefix; directive-only messages in the run are left for the existing
relocation. Unit tests cover the injected-style case, the string top-level
system case, mixed directive/text runs, and the no-op case.
Repro: POST /v1/messages with Claude Code client headers (user-agent
claude-cli/..., x-app: cli), model claude-opus-5, a top-level system, one tool,
and messages[0] = {role: "system", content: "[OmniRoute Output Styles] ..."}.
Before: 400 from Anthropic. After: 200.
diegosouzapw
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Sep 24, 2026
…souzapw#13887 fix Restore every file except accountFallback.ts and its test to the release tip: the branch carried main-only content (diegosouzapw#13072 hoistLeadingTextSystemMessages in chatCore.ts and its test, model-catalog and usage-ordering changes) that the release does not have and that broke the merge train. Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>
diegosouzapw
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Sep 29, 2026
Brings the 12 main-only commits into the frozen release branch so the release PR (#11442) is no longer CONFLICTING. Most are main twins of fixes the release branch already carries in a newer shape; resolved by proving the release side contains them: - #12246 temp-dir retry: release uses cleanupTempDataDir / maxRetries (kept ours). - #11719 Bun image: release is already on oven/bun 1.4.2 (kept ours). - #12086 CVE-2025-68121 .trivyignore: dropped on release by #12429 (wreq-js). - #13865 npm 11 / electron overrides: release pins are newer (kept ours); the optional transformers webpack-ignore change merged cleanly. - streamTiming clock injection: release moved to a monotonic clock (kept ours). Real main-only fix ported: #13072 hoistLeadingTextSystemMessages, added to the release's claudeSystemRole.ts (the call site in chatCore.ts merged cleanly).
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What
On the Claude Code semantic passthrough path (provider
claude, 1M-context model,system+toolspresent), system-role messages are kept insidemessages[]and only directive-only messages are relocated offmessages[0]. Anthropic rejects a text-bearing system message atmessages[0]as well:That is exactly where the Output Styles injection lands (
outputStyles/apply.tsunshifts a system message), so with an output style active every Claude Code turn on such a model returns 400.Fix
hoistLeadingTextSystemMessages()inopen-sse/handlers/chatCore/claudeSystemRole.ts: move only the leading run of text-bearing system-role messages (everything before the first user/assistant turn) into the top-levelsystemparameter, called beforerelocateDirectiveOnlyMessages()on that path. Genuine mid-conversation system turns keep their position and cache prefix; directive-only messages in the leading run are left to the existing relocation. An existing top-levelsystem(string or blocks) is preserved and the hoisted blocks are appended.Tests
tests/unit/claude-leading-text-system-hoist.test.ts: injected-style case, string top-level system, mixed directive/text leading run (combined with the relocation), and the no-op case. The existing directive-only and mid-conversation passthrough tests still pass.Repro
POST /v1/messageswith Claude Code client headers (user-agent: claude-cli/...,x-app: cli), modelclaude-opus-5, a top-levelsystem, one tool, andmessages[0] = {role: "system", content: "[OmniRoute Output Styles] ..."}followed by a user turn. Before: 400 from Anthropic. After: 200. Running on a self-hosted instance since 2026-09-04.🤖 Generated with Claude Code