[WRONG BRANCH] fix: keep hidden reasoning out of transparent envelopes

[luvs01]

Motivation

• The previous change encoded suppressed thinking text into a base64 ocxr1: envelope and later decoded it, which exposed hidden chain-of-thought to clients and downstream adapters.
• The goal is to preserve opaque provider state (signatures, redacted blobs, Kiro ciphertext) without leaking suppressed plaintext reasoning or restoring it into assistant messages.

Description

• Stop including plaintext txt in reasoning envelopes by removing txt from ReasoningEnvelope and ensuring encodeReasoningEnvelope/decodeReasoningEnvelope only carry sig, red, and krc as opaque payloads (see src/responses/reasoning-envelope.ts).
• Prevent the bridge from serializing suppressed thinking or raw reasoning text into encrypted_content when hideThinkingSummary is enabled, while keeping the signature and redacted blocks round-tripable (see src/bridge.ts).
• Stop restoring legacy plaintext envelope txt into assistant thinking content during parsing so legacy/plaintext envelopes no longer become replayed assistant thinking (see src/responses/parser.ts).
• Preserve internal replay behavior for tool-call replay (replay cache kept) while ensuring hidden text is not emitted in responses; update tests to assert no hidden-text leakage and preserve signature/redaction semantics (tests updated in tests/anthropic-thinking-signature.test.ts and tests/bridge-raw-reasoning-hidden.test.ts).

Testing

• Ran bun run typecheck and bun run privacy:scan, both succeeded.
• Ran targeted tests with bun test tests/anthropic-thinking-signature.test.ts tests/bridge-raw-reasoning-hidden.test.ts tests/bridge.test.ts, which exercise the ocxr1 envelope, hidden reasoning, and bridge behavior; the modified tests covering hidden-text leakage and envelope handling passed; the test run reported one environment-specific failure unrelated to these changes (node:zlib.zstdDecompressSync missing in the active Bun runtime).
• Performed broader bun run test locally to validate integration scope; the changed areas exercised by the suite passed, with an unrelated external-proxy timeout observed in the long-running portion of the full suite.

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📥 Commits

Reviewing files that changed from the base of the PR and between 57140d6 and a9d9aec.

📒 Files selected for processing (5)

• src/bridge.ts
• src/responses/parser.ts
• src/responses/reasoning-envelope.ts
• tests/anthropic-thinking-signature.test.ts
• tests/bridge-raw-reasoning-hidden.test.ts

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✅ Deterministic PR hygiene checks passed.

[github-actions]

⏳ DRAFT

• wrong target branch (main); retarget to dev.

What to do

• Retarget this PR to dev — all contributions go to dev.

Its title has been prefixed with [WRONG BRANCH].
This pull request was already a draft. Its draft status will be preserved after every issue above is resolved.