A structural engine (ccr / session-dedup) that finds nothing to compress
returns the body unchanged. That no-op was mishandled three ways — the
code-level root cause of the #6465–#6493 "0% savings, no reason" symptom class:
A. Inflation guard mislabelled a no-op as inflation. guardPipelineInflation
used `compressedTokens >= originalTokens`, so an unchanged body
(compressedTokens === originalTokens) tripped the guard, setting
fallbackApplied=true and emitting a misleading "did not shrink; reverted
to original" warning. Changed to strict `>` — only a strictly larger
output is inflation; equality is a no-op. Genuine inflation still reverts.
B. Disabled-engine skip was silent and asymmetric with the breaker skip. Both
stacked loops (sync + async) skipped a registry-disabled engine with a bare
`continue`, recording no validationWarning — while the sibling breaker-open
branch does. Both loops now add
`${engine}: skipped (engine disabled in registry)`, mirroring the breaker branch.
C. No-op engine lost its identity in engineBreakdown. mergeStackStep
early-returned on null stats, pushing no breakdown entry, so
ensureEngineBreakdown synthesized a generic "stacked" 0% node. It now records
a zero-savings entry keyed on the engine that actually ran, preserving identity.
Tests: tests/unit/compression-noop-guard.test.ts covers A (equal-token no-op not
inflated; strictly-larger still reverts), B (disabled skip surfaces a "disabled"
warning), and C (no-op engine keeps its own id in the breakdown). Updated the
existing inflation-guard test whose net-zero case encoded the old buggy behaviour,
and switched its wire test to object-form pipeline steps so the intended engine runs.
Co-authored-by: Chirag Singhal <chirag127@users.noreply.github.com>
Co-authored-by: Diego Rodrigues de Sa e Souza <diegosouza.pw@gmail.com>
Co-authored-by: Diego Rodrigues de Sa e Souza <8016841+diegosouzapw@users.noreply.github.com>
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