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docs: clarify SEP-2243 HeaderMismatch error code#2992

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DaleSeo:docs/clarify-sep-2243-header-mismatch-code
Jul 21, 2026
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docs: clarify SEP-2243 HeaderMismatch error code#2992
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modelcontextprotocol:mainfrom
DaleSeo:docs/clarify-sep-2243-header-mismatch-code

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@DaleSeo DaleSeo commented Jun 30, 2026 •
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Fixes #2991

Motivation and Context

SEP-2243 still documented HeaderMismatch as -32001, but the current draft specification and schema use -32020 after the error-code renumbering in #2907.

SEP-2243 Draft Spec
2026-06-30 at 09 32 28 2026-06-30 at 09 30 35

This updates the SEP text, examples, and conformance tables to use -32020, and adds a note explaining that SEP-2243 originally assigned HeaderMismatch to -32001 before the draft spec renumbered it.

How Has This Been Tested?

Documentation-only change.

Breaking Changes

None.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

This came up during modelcontextprotocol/rust-sdk#907.

@DaleSeo
DaleSeo requested review from a team as code owners June 30, 2026 13:19
@DaleSeo
DaleSeo force-pushed the docs/clarify-sep-2243-header-mismatch-code branch from c709ed8 to 8330e83 Compare June 30, 2026 13:26
@localden localden mentioned this pull request Jul 4, 2026
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@localden localden added the rc-high-priority Related to an upcoming specification release and needs to be addressed with a high priority. label Jul 10, 2026
@DaleSeo
DaleSeo force-pushed the docs/clarify-sep-2243-header-mismatch-code branch from 8330e83 to 0eb48f4 Compare July 14, 2026 12:15
@DaleSeo

DaleSeo commented Jul 14, 2026

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@localden @dsp-ant Any chance we can get this PR reviewed? I can't request a review on another one, #3092, because of the open pull request limit.

dsp-ant
dsp-ant requested changes Jul 16, 2026
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Thank you. I appreciate this. I do think however that we should keep the SEP as is, as a document. We might want to add at the bottom a "Changed Since": or something like that, but not change the original documented that core maintainers voted on. Thoughts @localden ?

@DaleSeo

DaleSeo commented Jul 16, 2026

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@dsp-ant I understand the value in preserving SEPs as documents but one thing to consider is that outdated information on SEP pages can mislead coding agents. For example, I discovered this discrepancy while implementing the SEP in modelcontextprotocol/rust-sdk#907 (comment). So, I think it would be helpful to mention this somewhere on the SEP page.

@dsp-ant

dsp-ant commented Jul 16, 2026

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@dsp-ant I understand the value in preserving SEPs as documents but one thing to consider is that outdated information on SEP pages can mislead coding agents. For example, I discovered this discrepancy while implementing the SEP in modelcontextprotocol/rust-sdk#907 (comment). So, I think it would be helpful to mention this somewhere on the SEP page.

I think I am okay if we add a section at the bottom saying:

## Changes since SEP became Final
...describe the changes

or something along those lines.

@DaleSeo
DaleSeo force-pushed the docs/clarify-sep-2243-header-mismatch-code branch from 0eb48f4 to 2cb1cc0 Compare July 16, 2026 19:09
@DaleSeo
docs: add 'Changes since SEP became Final' section to SEP-2243
8767681 
Preserve SEP-2243 as a historical record instead of editing its body,
and document the HeaderMismatch error code reassignment from -32001 to
-32020 (modelcontextprotocol#2907) in a dedicated section per maintainer feedback.

Also regenerate SEP-2549 docs, whose rendered mdx had drifted from its
source on main, so 'npm run check:seps' passes on PR CI.
@DaleSeo
DaleSeo force-pushed the docs/clarify-sep-2243-header-mismatch-code branch from 28a285e to 8767681 Compare July 16, 2026 21:07
@DaleSeo

DaleSeo commented Jul 16, 2026

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Thanks for the guidance, @dsp-ant. I undid the inline edits and added the section.

@DaleSeo
DaleSeo requested a review from dsp-ant July 16, 2026 21:10
dsp-ant
dsp-ant approved these changes Jul 21, 2026
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Thank you @DaleSeo

@dsp-ant
dsp-ant merged commit e0a4653 into modelcontextprotocol:main Jul 21, 2026
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SEP-2243 still references pre-renumber HeaderMismatch error code -32001

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@DaleSeo @dsp-ant @localden