Add captcha task-start and challenge-result events (#332)

## Summary

- add task-level `captcha_solve_started` and challenge-level
`captcha_challenge_result` telemetry
- distinguish challenge outcomes as `solved`, `failure`, `timeout`, or
`abandoned`
- require `data` on both new events and `duration_ms` on challenge
results
- preserve the existing generated captcha type and solve-result status
symbols for downstream Go consumers

## Contract

`captcha_solve_started` records that a solver accepted one task.
`task_id` pairs that start with its terminal `captcha_solve_result`,
while `challenge_id` groups every task from one visible challenge.
Delivery remains best-effort and unordered, so event arrival or absence
does not indicate current solve state.

`captcha_challenge_result` is emitted once for the visible challenge.
`failure` means the producer reached an explicit terminal solver failure
or exhausted its attempts while the challenge remained. `timeout` is
reserved for an actual challenge-level wait budget. `abandoned` covers
observation ending without either a solved signal or an explicit
terminal solver outcome.

The shared captcha taxonomy keeps the legacy generated
`BrowserCaptchaSolveResultEventDataCaptchaType` name and constants
through a schema alias. Existing relay code therefore compiles unchanged
when it updates this module.

## Rollout

Schema and generated image API types only; no producer behavior changes
here. The public API schema and extension producer are updated in their
corresponding PRs before consumers rely on the new challenge event.

## Testing

- `go test ./lib/oapi ./lib/events/...` — pass, including
generated-symbol and required-field compatibility coverage
- `go build ./...` — pass
- `go vet ./...` — pass
- OpenAPI generation run twice — byte-identical generated output
- `go test ./lib/capmonsterrelay` on `kernel/kernel#3432` with this
module replacement — pass without relay changes
- GitHub `test-server-e2e` — all cases except
`TestReplayRecordingIncludesAudioTrack`; that unrelated test failed
twice because the generated audio track ended 0.38s / 1.29s before its
recording-duration threshold. The base branch has a green full e2e run
on the same base commit.

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Author: archandatta

server/lib/events/category_gen.go

@@ -21,6 +21,16 @@ func TestCategoryMapsAgreeOnAPICallSplit(t *testing.T) {
 	assert.Equal(t, Platform, cat)
 }
 
+func TestCaptchaCategories(t *testing.T) {
+	for _, eventType := range []string{"captcha_solve_started", "captcha_challenge_result"} {
+		t.Run(eventType, func(t *testing.T) {
+			cat, ok := CategoryForType(eventType)
+			require.True(t, ok)
+			assert.Equal(t, Captcha, cat)
+		})
+	}
+}
+
 func TestCategoryForOperation(t *testing.T) {
 	require.NotEmpty(t, categoryByOperationID, "generator produced no operations")
 

server/lib/events/category_test.go

@@ -0,0 +1,48 @@
+package oapi
+
+import "testing"
+
+func TestCaptchaGeneratedNamesRemainCompatible(t *testing.T) {
+	var captchaType BrowserCaptchaSolveResultEventDataCaptchaType = BrowserCaptchaSolveResultEventDataCaptchaTypeHcaptcha
+	var sharedType BrowserCaptchaType = captchaType
+	if sharedType != captchaType {
+		t.Fatalf("shared captcha type = %q, want %q", sharedType, captchaType)
+	}
+
+	statuses := []BrowserCaptchaSolveResultEventDataStatus{
+		Success,
+		Failure,
+		Timeout,
+		Abandoned,
+	}
+	for _, status := range statuses {
+		if !status.Valid() {
+			t.Fatalf("solve status %q is invalid", status)
+		}
+	}
+	for _, status := range []BrowserCaptchaChallengeResultEventDataStatus{
+		ChallengeSolved,
+		ChallengeFailure,
+		ChallengeTimeout,
+		ChallengeAbandoned,
+	} {
+		if !status.Valid() {
+			t.Fatalf("challenge status %q is invalid", status)
+		}
+	}
+
+	started := BrowserCaptchaSolveStartedEvent{
+		Data: BrowserCaptchaSolveStartedEventData{CaptchaType: captchaType},
+	}
+	challenge := BrowserCaptchaChallengeResultEvent{
+		Data: BrowserCaptchaChallengeResultEventData{
+			CaptchaType: captchaType,
+			ChallengeId: "challenge-id",
+			DurationMs:  1,
+			Status:      ChallengeFailure,
+		},
+	}
+	if started.Data.CaptchaType != challenge.Data.CaptchaType {
+		t.Fatal("captcha event types are inconsistent")
+	}
+}