Expose GitHub search quotas and MCP 429 retry hints (#68728)

* Initial plan

* Log GitHub search quotas and surface MCP HTTP 429 retry hints

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Preserve MCP Retry-After hints that resemble HTTP status codes

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Wrap MCP 429 hints in collapsible summary

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Apply remaining changes

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Fix MCP retry hints and gate quota snapshots

Co-authored-by: gh-aw-bot <259018956+gh-aw-bot@users.noreply.github.com>

* Preserve unified MCP rate-limit evidence and complete review fixes

Harden echoed-query masking, resolve quota probes from the actual MCP tool set, and persist sanitized HTTP 429 retry hints alongside GitHub quota snapshots in the unified session.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Isolate MCP retry parsing and refresh quota snapshot goldens

Keep unified session normalization independent of gateway summary logging shims, and record the intended agent-start/end quota steps in WASM fixtures.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: gh-aw-bot <259018956+gh-aw-bot@users.noreply.github.com>
Co-authored-by: pelikhan <jhalleux@microsoft.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: 4 people