fix(mcp): webhook envelope profile falls back to active profile (KLA-420)

[jklaassenjc]

Summary

KLA-420 — surfaced during the 1.17.0 code-quality review.

In 1.17.0 (KLA-413), server.go wired stepUpConfig.Profile = opts.SigningProfile directly. The signer block beneath it falls back to config.ActiveProfile() when SigningProfile == "", but the webhook path didn't. Result: an operator who enables

```yaml
mcp:
require_step_up_for_destructive: true
step_up_authenticator: webhook
approval_webhook_url: ...
```

without also enabling mcp.sign_destructive_ops gets "profile": "" in every outbound approval envelope. Receivers keying on profile (Slack bot routing, audit dashboards) see empty strings instead of the active profile name.

Fix

Resolve the profile once at the server level, before building both stepUpConfig and the signer:

```go
profile := opts.SigningProfile
if profile == "" {
profile = config.ActiveProfile()
}
```

SigningProfile remains the explicit opt-in; empty means "use the active profile" and now applies uniformly to both consumers.

Tests

• TestNewServer_WebhookProfileFallsBackToActiveProfile — empty SigningProfile → webhook authenticator profile = "default"
• TestNewServer_WebhookProfileHonorsExplicitSigningProfile — "staging" → webhook authenticator profile = "staging"

Test plan

• go test ./internal/mcp/ ./internal/cmd/ green
• go vet ./... clean
• Both new tests pass; existing webhook + signer tests unchanged

🤖 Generated with Claude Code

---

Note

Low Risk
Small, localized server bootstrap change with regression tests; no auth or approval-gate logic changes beyond metadata in outbound envelopes.

Overview
KLA-420: Webhook step-up approval envelopes now get the same profile resolution as the destructive-op signer.

NewServer resolves profile once (SigningProfile, or config.ActiveProfile() when empty) and passes it into both stepUpConfig and the signer. Previously only the signer path fell back to the active profile, so webhook-only destructive approval (require_step_up + webhook, without sign_destructive_ops) posted "profile": ""—breaking Slack routing and audit views that key on profile.

Tests assert empty SigningProfile → active profile (default) on webhookStepUp, and explicit SigningProfile → that value unchanged.

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