Normalize proxyMode to always reflect effective HTTP protocol

[ChrisJBurns]

Summary

• proxyMode was only meaningful for stdio transports but could be set on any transport type, returning empty or misleading values to API consumers, vMCP, Optimizer, and the UI. Every client had to implement conditional logic via GetEffectiveProxyMode() to determine the actual protocol in use.
• Normalize proxyMode at write boundaries (config builder and config load) so it always reflects the effective HTTP protocol. Also fixes the conflicting default in StdioTransport (defaulted to SSE while everything else defaulted to streamable-http).

Fixes #3296

Type of change

• Bug fix

Test plan

• Unit tests (task test)
• Linting (task lint-fix)

Changes

File	Change
pkg/transport/types/transport.go	Add EffectiveProxyMode() — canonical typed function that computes the actual HTTP protocol
pkg/transport/stdio.go	Fix conflicting default from SSE to streamable-http
pkg/runner/config.go	Add NormalizeProxyMode() method; call in ReadJSON for migration of existing configs
pkg/runner/config_builder.go	Call NormalizeProxyMode() at end of builder so all new configs are normalized
pkg/workloads/types/types.go	GetEffectiveProxyMode() now delegates to the canonical typed function
pkg/export/k8s.go	Remove unnecessary empty-check guard (proxyMode is always populated for stdio now)
pkg/transport/types/transport_test.go	10 test cases for EffectiveProxyMode
pkg/runner/config_test.go	7 test cases for NormalizeProxyMode

Does this introduce a user-facing change?

proxyMode in API responses and thv status output will now always be populated with the effective HTTP protocol, even for non-stdio transports. Previously it could be empty or misleading for sse/streamable-http transports.

Special notes for reviewers

• The existing 6 callers of GetEffectiveProxyMode() are now idempotent (normalizing an already-normalized value is a no-op). A follow-up PR can clean these up, but they are harmless to keep.
• The SSE default change in StdioTransport has no runtime impact — the factory always calls SetProxyMode() immediately after construction, overriding the default. The fix is for correctness and to prevent future bugs.
• Pre-existing persisted configs are migrated on load via the ReadJSON normalization, requiring no explicit data migration.

Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.65%. Comparing base (e69251a) to head (e665c96).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/transport/stdio.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4468   +/-   ##
=======================================
  Coverage   69.64%   69.65%           
=======================================
  Files         491      491           
  Lines       50304    50310    +6     
=======================================
+ Hits        35036    35043    +7     
  Misses      12580    12580           
+ Partials     2688     2687    -1     

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