Replace opaque Step A/B labels in XAA CRD comments

[jhrozek]

Summary

The XAASpec struct comments and the generated CRD YAML descriptions used
"Step A" and "Step B" to refer to the two phases of the ID-JAG protocol.
These labels are opaque — they tell the reader nothing about what each step
does or which endpoint it targets, and they're easy to confuse with each
other.

Replace them throughout with action-oriented names:

• IdP exchange — RFC 8693 token exchange at the user's IdP; produces the ID-JAG JWT
• target grant — RFC 7523 JWT bearer grant at the target AS; produces the backend access token

The rename covers:

• MCPExternalAuthConfig's XAASpec (ExternalAuthTypeXAA const comment, the
  type comment, and every field description referencing the old labels).
• pkg/vmcp/auth/types.XAAConfig — the runtime config struct that also feeds
  the VirtualMCPServer CRD schema (via Spec.Config.OutgoingAuth.Backends[].XAA).
  Left un-renamed initially, this would have made kubectl explain show two
  different names for the same protocol concept depending on which CRD you
  asked.
• pkg/vmcp/auth/strategies/xaa.go — the XAAStrategy implementation:
  doc comments, slog debug/warn log strings, wrapped error messages, and the
  performStepA/performStepB function names (now performIDPExchange/
  performTargetGrant).
• Two incidental mentions in the generic pkg/oauthproto/jwtbearer and
  pkg/oauthproto/tokenexchange packages that referenced XAA's steps as an
  example use case.

CRD YAML and the CRD API reference docs (docs/operator/crd-api.md)
regenerated with task operator-manifests and task crdref-gen.

Type of change

• Documentation update (no production code change)

Test plan

• task operator-manifests and task crdref-gen ran cleanly; grep -rc "Step A\|Step B" across the repo (.go, .yaml, .md) returns zero matches everywhere, including the VirtualMCPServer CRD (toolhive.stacklok.dev_virtualmcpservers.yaml) and docs/operator/crd-api.md
• task lint-fix — 0 issues
• task test — full unit suite passes

Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 70.61%. Comparing base (2aca563) to head (091392a).

Files with missing lines	Patch %	Lines
pkg/vmcp/auth/strategies/xaa.go	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5703      +/-   ##
==========================================
- Coverage   70.63%   70.61%   -0.02%     
==========================================
  Files         667      667              
  Lines       67607    67607              
==========================================
- Hits        47752    47742      -10     
- Misses      16399    16411      +12     
+ Partials     3456     3454       -2     

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[JAORMX]

Multi-agent panel review 🤖

Reviewed by a 4-axis panel (comment-vs-code accuracy · CRD generated-file consistency · OAuth/XAA protocol domain · doc clarity). Non-blocking COMMENT.

Consensus: approve-with-nits. Within the diff's scope everything checks out — the new labels are protocol-accurate (RFC 8693 "IdP exchange" / RFC 7523 "target grant", verified field-by-field against xaa.go), the Go godoc and both generated CRD YAMLs are byte-consistent, and the diff is reproducible by controller-gen with no hand-editing. Using distinct verbs — exchange (8693) vs grant (7523) — genuinely encodes the two OAuth mechanisms rather than just renaming; nice call.

The one substantive issue is that the rename is incomplete.

Main finding — incomplete rename (all four axes flagged this; doc-clarity rated it high)

The identical XAA "Step A/B" vocabulary still lives in two other places the PR didn't touch:

• pkg/vmcp/auth/types/types.go:270-325 — a structurally-identical XAA config struct that is the controller-gen source for the VirtualMCPServer CRD. Its generated virtualmcpservers.yaml (both the files/crds and templates copies, ~24 occurrences each) still says "Step A (RFC 8693)" / "Step B (RFC 7523)".
• pkg/vmcp/auth/strategies/xaa.go:32-33, 82, 125-141, 176 — the strategy godoc, performStepA/performStepB, and debug/error log strings.

After merge, kubectl explain mcpexternalauthconfig...xaa will show "IdP exchange / target grant" while kubectl explain virtualmcpserver...xaa — describing the same ID-JAG two-step exchange — still shows "Step A/B". Two names for one concept is exactly the confusion this PR set out to remove.

Suggested resolution: extend the identical rename to types.go (and xaa.go), regenerate, and include the virtualmcpservers.yaml deltas here — or, if this is intentionally a scoped first step, say so in the PR body and file the follow-up so it isn't silently left half-done.

Minor / nits

• PR body test-plan claim — "generated YAML contains zero occurrences of 'Step A' or 'Step B'" is true only for mcpexternalauthconfigs.yaml; virtualmcpservers.yaml still contains them. Worth qualifying to the specific CRD.
• mcpexternalauthconfig_types.go (~L1380) — lone "sent as the resource parameter in the IdP exchange"; every other new usage is article-less ("in IdP exchange"). Drop the article for consistency.
• mcpexternalauthconfig_types.go (~L1338) — bullet "Target grant (RFC 7523)" uses capital-T while the canonical inline label is lowercase "target grant"; lowercase to match, or accept as sentence-case.
• Label-basis asymmetry: "IdP exchange" (named by endpoint) vs "target grant" (named by grant type) — accurate, but "target grant" is coined shorthand rather than draft/RFC terminology.

_{Generated with Claude Code — multi-agent panel review.}