fix(agents-core): prevent metadata header pollution and preserve base headers in CredentialStuffer

[Adityakk9031]

Summary

This PR fixes two critical issues in \CredentialStuffer.prototype.getCredentialHeaders:

1. Metadata Header Pollution: In \CredentialStuffer.ts, \credentialStoreHeaders.metadata\ (which contains arbitrary non-string data such as nested objects, arrays, booleans, and numbers) was being spread directly into HTTP headers. This causes runtime \TypeError\ / malformed header exceptions in HTTP/fetch/undici clients when calling MCP servers.
2. Base Header Loss: If a tool had custom base \headers\ defined alongside a \storeReference, the base headers were lost in the merged output. Fixed to preserve base headers, credential store headers, and template headers cleanly.

Verification

• \pnpm --filter @inkeep/agents-core test src/tests/credentials/credentialStuffer.test.ts\ passes (23/23 tests pass).
• \pnpm --filter @inkeep/agents-core typecheck\ passes with zero errors.

[changeset-bot]

🦋 Changeset detected

Latest commit: fbe47c1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 10 packages

Name	Type
@inkeep/agents-core	Patch
@inkeep/agents-work-apps	Patch
@inkeep/ai-sdk-provider	Patch
@inkeep/create-agents	Patch
@inkeep/agents-api	Patch
@inkeep/agents-manage-ui	Patch
@inkeep/agents-cli	Patch
@inkeep/agents-email	Patch
@inkeep/agents-mcp	Patch
@inkeep/agents-sdk	Patch

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[github-actions]

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[Adityakk9031]

@robert-inkeep have a look

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity.
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[Adityakk9031]

@tim-inkeep please have a look

[Adityakk9031]

working

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity.
It will be closed in 7 days if no further activity occurs.

If this PR is still relevant:

• Rebase it on the latest main branch
• Add a comment explaining its current status
• Request a review if it's ready

Thank you for your contributions!

[Adityakk9031]

@dimaMachina have a look

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity.
It will be closed in 7 days if no further activity occurs.

If this PR is still relevant:

• Rebase it on the latest main branch
• Add a comment explaining its current status
• Request a review if it's ready

Thank you for your contributions!

[Adityakk9031]

still working

[Adityakk9031]

@nick-inkeep have a look