[Juliusolsson05]

What

Routes switchProvider's translation through the neutral-hub codec seam instead of calling the pairwise converters directly:

toClaude(codexLines, opts)   -> translateToClaude(CodexCodec.decode(codexLines), opts).lines
toCodex(claudeEntries, opts) -> translateToCodex(ClaudeCodec.decode(claudeEntries), opts).lines

Byte-identical to the old direct calls: codec decode wraps every source record in the lossless passthrough region, translateTo* reconstructs that exact source array and runs the same legacy converter with the same options. Pinned by atp's testing/translate-equivalence.ts (ClaudeCodec.encode(CodexCodec.decode(x)) ≡ toClaude(x) and the symmetric case), which I ran green against the pinned atp commit b50d73f.

Why a byte-identical refactor

switchProvider becomes the first production consumer of the neutral hub. When the atp engine migrates to true per-entry neutral translation (a later slice, verified against the same corpus), provider switching inherits it with zero further edits — and a third provider's codec makes its switch pairs work here for free.

This deliberately isolates the safe seam swap from the more delicate work: the resume sanitizers (claudeResumeSanitizer/codexResumeSanitizer) and id/file-layout policy stay app-side. Absorbing them into the codecs is the separate, riskier slice (#394 phase 5b) that this one de-risks by landing the seam first. duplicateSession/rewindSession follow the same pattern and are follow-ups.

Verification

• verify:neutral-translate (atp, at pinned commit) → all codex↔claude equivalences hold, fidelity + lossy
• tsc -p tsconfig.node.json → 0 · tsc --noEmit -p tsconfig.web.json → 0
• electron-vite build ✓ · npm test → 170/170 (1 pre-existing voice-dictation "No test suite found" quirk)

🤖 Generated with Claude Code