fix: eight protocol/transport defects in MCP 2.0 negotiation, replay, and bridging

[steipete]

Fixes eight protocol/transport defects found by an adversarial review of the MCP 2.0 series (#254–#258) and by testing against 30+ public MCP servers in the wild. Every fix ships with a regression test that fails before and passes after.

Negotiation

• SSE fallback no longer inherits modern negotiation. SSE is a legacy-era transport, but the fallback reused the modern-negotiating client. Consequences: auto mode re-sent server/discover on the SSE attempt (breaking legacy SSE-only servers), and pin mode masked the SDK's accurate error behind a meaningless SSE error: Non-200 status code (405). Verified in the wild: pinning 2026-07-28 at Context7 now reports "the server did not offer pinned protocol version 2026-07-28 via server/discover (no fallback in pin mode)". The fallback site now builds a legacy client via a small HttpClientFactory seam rather than threading flags.
• stdio auto-negotiation can now recover from strict legacy servers. Because McporterStdioTransport subclasses the SDK transport, the probe runs in-place on the only process; a legacy server that exits on any pre-initialize request left nothing to fall back to. Auto mode now retries once with a fresh legacy process. Modern servers keep the single-spawn fast path.
• stdio probe timeout raised from 3s to the SDK default (60s), configurable via MCPORTER_STDIO_PROBE_TIMEOUT_MS. The old 3s budget included process cold-start and misclassified slow modern servers as legacy.

Record/replay

• RecordTransport now mirrors the wrapped transport's full capability surface. It was dropping hasPerRequestStream, so the v2 client never attached requestSignal and on timeout emitted the removed notifications/cancelled while the HTTP request kept running.
• Replay honors the caller's elicitation handler instead of force-installing a decline responder, so recordings whose MRTR round was accepted can actually replay.
• Recorded inbound notifications (progress, logging, list-changed) are re-emitted in order instead of being silently dropped.

Bridge & pagination

• The dual-era bridge preserves non-object output schemas and projects results per era via the SDK's own projectCallToolResult. Previously outputSchema: {type:"number"} was dropped on both eras and a v1 client's call failed -32602 expected record, received number.
• Resource pagination detects a repeated/non-advancing cursor instead of issuing 100 requests and appending the same page 99 times.

Proof: pnpm check clean; 955 passed / 3 skipped; autoreview clean (0.96). Re-verified against live servers across all four eras (2025-03-26 → 2026-07-28) with no regressions.

🤖 Generated with Claude Code

[clawsweeper]

ClawSweeper status: review started.

I am starting a fresh review of this pull request: fix: eight protocol/transport defects in MCP 2.0 negotiation, replay, and bridging This is item 1/1 in the current shard. Shard 0/1.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Don't fall back to legacy when modern is pinned

When a server is configured with protocolVersion: '2026-07-28', any primary Streamable HTTP error that is not tagged EraNegotiationFailed still reaches this fallback and creates a forced-legacy SSE client. For pinned-modern definitions, a 404/405 transport mismatch or similar primary failure can therefore silently connect and run calls in the 2025-era protocol even though the config says 2026-07-28 is required; skip the SSE fallback for pinned definitions rather than only for one error code.

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