Add proxy handoff for exhausted sequences

[andrespaez90]

Summary

• add a new proxy sequence end mode so exhausted sequences fall through to the configured backend target
• update the mock editor and sequence badges to expose and explain the new behavior in the UI
• add backend coverage for the exhausted-sequence handoff case

Why

Sequence mode already supports looping, staying on the last step, or returning the static fallback body. This change adds the missing passthrough behavior needed for flows where only the first N calls should be mocked and all subsequent calls should hit the real backend.

Implementation details

• extend Sequence.OnEnd with proxy
• make MatchAndResolve return nil once a proxy sequence is exhausted so the request can be proxied normally
• keep the frontend cursor logic aligned with backend behavior so the sidebar and editor correctly show when the next request will go to the real backend
• add a focused Go test covering the first mocked response and subsequent passthrough

Validation

• go test ./...
• npm run build

[Copilot]

Pull request overview

Adds a new “proxy” end mode for sequence mocks so that once all sequence steps have been served, subsequent matching requests are not resolved by the mock and instead fall through to the configured backend target. This extends existing sequence end behaviors (loop/stay/reset) and updates the frontend to accurately display the new passthrough behavior.

Changes:

• Extend sequence on_end to support "proxy" and implement backend passthrough when exhausted.
• Update frontend sequence cursor/display logic, sidebar badges/tooltips, and editor controls to expose “proxy after end”.
• Add a focused Go test verifying first-step resolution and subsequent passthrough for proxy sequences.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
mock.go	Implements on_end: "proxy" behavior in MatchAndResolve and updates sequence end-mode handling.
mock_test.go	Adds backend test ensuring exhausted proxy sequences fall through (return nil).
frontend/src/types.ts	Extends Sequence.on_end union to include 'proxy'.
frontend/src/sequence.ts	Keeps cursor/label logic aligned with backend behavior and adds proxy “next call” display.
frontend/src/components/Sidebar.tsx	Updates sidebar status tooltip and sequence fallback-status explanation for proxy mode.
frontend/src/components/MockEditorModal.tsx	Adds “Proxy after end” option and editor status text for exhausted proxy sequences.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.