revert: mid-stream fallback (#882)

[jarvis9443]

Reverts #882. The mid-stream continuation feature is paused pending re-evaluation of the requirement — see api7/AISIX-Cloud#1222 (feature never shipped in a release, so no user-visible change). Ref api7/AISIX-Cloud#1222

Summary by CodeRabbit

• Breaking Changes
  • Removed mid-stream fallback and continuation handling for streaming responses.
  • Removed routing configuration for stream failure behavior.
  • Removed stream outcome details from usage events and related fallback metrics.
  • Updated routing and model schemas to no longer expose stream failure settings.
• Bug Fixes
  • Simplified streaming completion and telemetry behavior by eliminating mid-stream failover classifications.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 983bfa3c-8b96-486f-a39b-11aaf3e80e73

📥 Commits

Reviewing files that changed from the base of the PR and between 6de5738 and b39ad41.

📒 Files selected for processing (13)

• crates/aisix-admin/src/openapi.rs
• crates/aisix-core/src/lib.rs
• crates/aisix-core/src/models/mod.rs
• crates/aisix-core/src/models/routing.rs
• crates/aisix-obs/src/metrics.rs
• crates/aisix-obs/src/usage.rs
• crates/aisix-proxy/src/chat.rs
• crates/aisix-proxy/src/lib.rs
• crates/aisix-proxy/src/routing.rs
• crates/aisix-proxy/src/stream_failover.rs
• schemas/resources/model.schema.json
• schemas/resources/routing.schema.json
• tests/e2e/src/cases/mid-stream-fallback-e2e.test.ts

💤 Files with no reviewable changes (10)

• crates/aisix-proxy/src/routing.rs
• schemas/resources/model.schema.json
• crates/aisix-obs/src/usage.rs
• crates/aisix-admin/src/openapi.rs
• crates/aisix-core/src/models/routing.rs
• tests/e2e/src/cases/mid-stream-fallback-e2e.test.ts
• schemas/resources/routing.schema.json
• crates/aisix-proxy/src/stream_failover.rs
• crates/aisix-obs/src/metrics.rs
• crates/aisix-proxy/src/lib.rs

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📝 Walkthrough

Walkthrough

The change removes mid-stream failure configuration, failover execution, continuation handling, related telemetry, schema definitions, OpenAPI mappings, and end-to-end coverage.

Changes

Mid-stream failover removal

Layer / File(s)	Summary
Routing contracts and schemas crates/aisix-core/src/models/routing.rs, crates/aisix-core/src/models/mod.rs, crates/aisix-core/src/lib.rs, schemas/resources/model.schema.json, schemas/resources/routing.schema.json, crates/aisix-admin/src/openapi.rs, crates/aisix-proxy/src/routing.rs	Removes mid-stream failure routing types, fields, exports, schema definitions, OpenAPI mappings, and fixture initialization.
Streaming execution and telemetry crates/aisix-proxy/src/chat.rs, crates/aisix-proxy/src/stream_failover.rs, crates/aisix-proxy/src/lib.rs, crates/aisix-obs/src/metrics.rs, crates/aisix-obs/src/usage.rs, tests/e2e/src/cases/mid-stream-fallback-e2e.test.ts	Removes failover state, continuation requests, failed-attempt accounting, stream outcome fields, fallback metrics, the failover module, and its end-to-end tests. Streaming completion retains existing reservation accounting and error-frame handling.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• api7/aisix#882: Introduced the mid-stream fallback functionality removed by this change.
• api7/aisix#893: Added and extended the same mid-stream failover functionality.
• api7/aisix#886: Modified the deleted stream_failover module.

Suggested reviewers: moonming

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states that the pull request reverts the mid-stream fallback feature and references the reverted pull request.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
E2e Test Quality Review	✅ Passed	The revert removes an unshipped feature, while existing E2E tests cover real etcd→gateway→HTTP-upstream flows for mid-stream timeout termination, no fallback, disconnects, and cancellation.
Security Check	✅ Passed	This PR safely reverts the mid-stream fallback feature by cleanly removing 1888 lines. No credentials, secrets, or PII are exposed; logging follows best practices with proper scoping of sensitive f...

✨ Finishing Touches

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• Commit unit tests in branch revert-882-midstream-fallback

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