feat(output-guard): last-line invariant on the response path — restore, log, never corrupt - #278
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feat(output-guard): last-line invariant on the response path — restore, log, never corrupt#278Gunther-Schulz wants to merge 5 commits into
Gunther-Schulz wants to merge 5 commits into
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…story rewrites stop busting the cache Claude Code re-serializes <system-reminder> hook blocks inside otherwise-stable user messages later in the session — moving one into its own message or merging it into a neighbour — which edits history mid-prefix and re-bills everything after the edit (reported independently as anthropics/claude-code#76606; measured here as the splice/insert-mid class, ~40 kB re-billed per unmitigated hit on a real session). The extension keeps a per-conversation canonical model of the message history keyed by content identity (message-hash.mjs: content hash + occurrence ordinal — position-independent, so repeated identical reminders stay distinct). Incoming volatile blocks are pinned to their first-seen serialization: when CC re-shapes an old reminder, the forwarded bytes keep the canonical form and the prefix survives. A history that stops matching the model (compaction, true rewrites) resets honestly rather than forcing a stale canon — pins survive the reset, order assumptions do not. Gated off by default: CACHE_FIX_INSERTION_NORMALIZE=1 enables normalization, CACHE_FIX_VOLATILE_PIN=1 the pinning. State persists under the state dir and survives proxy restarts. Measured on live traffic (513-request session, 2026-07-28): every observed splice/insert-mid pair forwarded with 0 re-billed bytes; the canonical-order invariant, cross-request stability and sequence gates all report 0 violations over 2.5 GB of captures. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
…e, log, never corrupt A pipeline of body-mutating extensions needs one check that runs LAST and answers a different question: is what we are about to send still the response the upstream sent, in every way the client depends on? The guard validates structural invariants (tool_use/tool_result adjacency among them) on the outbound response; on violation it RESTORES the original stashed by output-guard-stash (order 55, before any mutator) and logs the diff — a mutation bug becomes one logged line instead of a corrupted session. Its first 243 live firings were its own missing exemption, which is the point: a guard that can restore makes that class of mistake cheap to discover and free to survive. Gated: CACHE_FIX_OUTPUT_GUARD=1. Stacked on pr/insertion-normalization (imports validateToolAdjacency). The replay-classes fixtures are shared with pr/verification-tools — identical files, merge cleanly in either order. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This was referenced Jul 29, 2026
…ent (output slice of fork e0f8fcb) Path-scoped slice of fork commit e0f8fcb: the guard's fifth invariant (assistant-terminal) and its tests. The same commit's insertion-normalization tail guard belongs to the insertion slice (cnighswonger#272); this slice carries the extension only as a sync, in the following commit. Co-Authored-By: Claude opus-5 <noreply@anthropic.com>
… + tail guard Brings proxy/extensions/insertion-normalization.mjs and its real-pair test to the cnighswonger#272 slice tip (fork e0f8fcb) so this slice's output-guard invariant is exercised against the same insertion behaviour cnighswonger#272 ships. The pinned real-pair fixture is NOT part of this slice — the real-pair test skips without it, by design. Co-Authored-By: Claude opus-5 <noreply@anthropic.com>
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…ls-less tree skips, not dies The static harvest.mjs import defeated the file's own slice-portability idiom: in trees carrying only the extension (upstream cnighswonger#272/cnighswonger#278/cnighswonger#281) the whole file failed at module load, so the real-pair check never reached the skip it was designed to hit. The reader now loads like replayTools — dynamically, inside the test — and the fixture branch requires it, so tools-less trees skip with COULD NOT VERIFY. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01TcivCe2iLnKZxpB4qTXzEb
… fork da9bf8c Without tools/ the real-pair check now reaches its designed skip instead of dying at module load. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01TcivCe2iLnKZxpB4qTXzEb
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…cate is payload (insertion slice of fork e0f8fcb) Path-scoped slice of fork commit e0f8fcb: the insertion-normalization tail guard and its tests. The same commit's output-guard assistant-terminal invariant (proxy/extensions/output-guard.mjs, test/output-guard.test.mjs) belongs to the output-guard slice (cnighswonger#278) and is not part of this PR. Co-Authored-By: Claude opus-5 <noreply@anthropic.com>
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Pushed wave 2 for this slice — three commits. ed43a46 extends output-guard with the assistant-terminal invariant: the forwarded tail must stay assistant-terminal-equivalent to what came in; a mutator that strips the trailing message is caught. Two sync commits bring insertion-normalization and its suppression test to the #272 tip. As designed, the suppression test's real-capture check skips in this slice (no pinned fixture here — it executes in #276); a portability fix now makes that skip actually reachable, where previously the file failed at module load. Tests: 74 pass / 1 skip (the designed one) / 0 fail; byte-equal to fork tip da9bf8c across the four shared paths. 🤖 Generated with Claude Code |
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…cate is payload (insertion slice of fork e0f8fcb) Path-scoped slice of fork commit e0f8fcb: the insertion-normalization tail guard and its tests. The same commit's output-guard assistant-terminal invariant (proxy/extensions/output-guard.mjs, test/output-guard.test.mjs) belongs to the output-guard slice (cnighswonger#278) and is not part of this PR. Co-Authored-By: Claude opus-5 <noreply@anthropic.com>
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Why
Once a proxy runs body-mutating extensions (#272/#273, or any future one), the failure mode that matters most isn't a missed optimization — it's shipping a corrupted response. This guard is the last line: it runs after every mutator and asks a different question than any unit test can — is what we're about to send still the response upstream sent, in every way the client depends on?
What
output-guard-stash(order 55) stashes the pristine body before any mutator runs.output-guard(order 690) validates structural invariants on the outbound response (tool_use/tool_result adjacency among them). On violation it restores the stashed original and logs the diff — a mutation bug becomes one logged line instead of a broken session.CACHE_FIX_OUTPUT_GUARD=1.Evidence
10 tests, including gate 1: the guard fires zero times across every class-matrix corpus (a guard that fires on legitimate traffic trains its reader to ignore it — that's a failing guard, and its first 243 live firings on our fleet were exactly that: its own missing exemption, since fixed and pinned). Running in production alongside #272/#273 for two days, 0 safety violations across ~2.5 GB of daily replay.
🤖 Generated with Claude Code