[kernel-1116] rename capture session -> browser telemetry (#242)

## High Level Changes
- as per design `DELETE` endpoint is gone, stop telemetry is controlled
via setting all values to false ->
https://onkernel.slack.com/archives/C0B10F24TG9/p1778620560896099?thread_ts=1778586830.702399&cid=C0B10F24TG9
```
Endpoints:
- GET /telemetry — get current state (TelemetryState), 404 if not active
- PUT /telemetry — create/replace config (BrowserTelemetryConfig), returns 201 on start or 200 on replace
- PATCH /telemetry — update active config, 404 if not active
- POST /telemetry/events — publish an event into the bus
- GET /telemetry/stream — SSE stream of events, supports Last-Event-ID for resumption

Key schemas:
- BrowserTelemetryConfig — top-level config with a browser key → BrowserTelemetryCategoriesConfig
- BrowserTelemetryCategoriesConfig — four categories: console, network, page, interaction, each with { enabled: bool }
- Event — { ts, type, category, source, data, truncated }, category enum: console | network | page | interaction | system
- TelemetryState — { id, status (running|stopped), config, seq, created_at }
- PublishedEnvelope — { seq, event } — what the SSE stream and publish response return
```


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Moderate risk because it changes public API endpoints and refactors
the event pipeline to rely on new OpenAPI-generated types and a new
telemetry session lifecycle, which could impact event
delivery/compatibility.
> 
> **Overview**
> Replaces the `capture_session` API and internal `capturesession`
package with a new **browser telemetry** model (`GET/PUT/PATCH
/telemetry`) where telemetry is stopped by setting all categories to
`enabled:false` (no DELETE endpoint).
> 
> Renames/relocates event ingress and streaming to `POST
/telemetry/events` and `GET /telemetry/stream`, updates tests and e2e S2
storage coverage accordingly, and wires `cdpmonitor` to publish through
`TelemetrySession` (stamping `telemetry_session_id`).
> 
> Refactors the event schema to use OpenAPI-generated types
(`TelemetryEventCategory`, `BrowserEventSource`, typed `data` payloads),
adds `page_lcp` as a distinct event, and updates
screenshot/lifecycle/computed events to emit typed payloads and
process-monotonic sequencing.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
381ffa4. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: archandatta

server/Makefile

@@ -16,7 +16,7 @@ $(RECORDING_DIR):
 # 3. go mod tidy to pull deps
 oapi-generate:
 	pnpm i -g @apiture/openapi-down-convert
-	openapi-down-convert --input openapi.yaml --output openapi-3.0.yaml
+	openapi-down-convert --input openapi.yaml --output openapi-3.0.yaml --allOf
 	go tool oapi-codegen -config ./oapi-codegen.yaml ./openapi-3.0.yaml
 	@echo "Fixing oapi-codegen issue https://github.com/oapi-codegen/oapi-codegen/issues/1764..."
 	go run ./scripts/oapi/patch_sse_methods -file ./lib/oapi/oapi.go -expected-replacements 4

server/cmd/api/api/api.go

@@ -10,9 +10,9 @@ import (
 	"sync"
 	"time"
 
-	"github.com/kernel/kernel-images/server/lib/capturesession"
 	"github.com/kernel/kernel-images/server/lib/cdpmonitor"
 	"github.com/kernel/kernel-images/server/lib/devtoolsproxy"
+	"github.com/kernel/kernel-images/server/lib/telemetry"
 	"github.com/kernel/kernel-images/server/lib/events"
 	"github.com/kernel/kernel-images/server/lib/logger"
 	"github.com/kernel/kernel-images/server/lib/nekoclient"
@@ -81,13 +81,13 @@ type ApiService struct {
 	// when multiple CDP fast-path resizes fire in quick succession.
 	xvfbResizeMu sync.Mutex
 
-	// CDP event pipeline and cdpMonitor.
-	eventStream     *events.EventStream
-	captureSession  *capturesession.CaptureSession
-	cdpMonitor      cdpMonitorController
-	monitorMu       sync.Mutex
-	lifecycleCtx    context.Context
-	lifecycleCancel context.CancelFunc
+	// Telemetry event pipeline and CDP monitor.
+	eventStream      *events.EventStream
+	telemetrySession *telemetry.TelemetrySession
+	cdpMonitor       cdpMonitorController
+	monitorMu        sync.Mutex
+	lifecycleCtx     context.Context
+	lifecycleCancel  context.CancelFunc
 }
 
 var _ oapi.StrictServerInterface = (*ApiService)(nil)
@@ -98,8 +98,8 @@ func New(
 	upstreamMgr *devtoolsproxy.UpstreamManager,
 	stz scaletozero.PinnedController,
 	nekoAuthClient *nekoclient.AuthClient,
-	captureSession *capturesession.CaptureSession,
-	eventStream    *events.EventStream,
+	telemetrySession *telemetry.TelemetrySession,
+	eventStream      *events.EventStream,
 	displayNum int,
 ) (*ApiService, error) {
 	switch {
@@ -111,18 +111,18 @@ func New(
 		return nil, fmt.Errorf("upstreamMgr cannot be nil")
 	case nekoAuthClient == nil:
 		return nil, fmt.Errorf("nekoAuthClient cannot be nil")
-	case captureSession == nil:
-		return nil, fmt.Errorf("captureSession cannot be nil")
+	case telemetrySession == nil:
+		return nil, fmt.Errorf("telemetrySession cannot be nil")
 	case eventStream == nil:
 		return nil, fmt.Errorf("eventStream cannot be nil")
 	}
 
-	mon := cdpmonitor.New(upstreamMgr, captureSession.Publish, displayNum, slog.Default())
+	mon := cdpmonitor.New(upstreamMgr, telemetrySession.Publish, displayNum, slog.Default())
 	ctx, cancel := context.WithCancel(context.Background())
 
 	return &ApiService{
-		recordManager:   recordManager,
-		factory:         factory,
+		recordManager:     recordManager,
+		factory:           factory,
 		defaultRecorderID: "default",
 		watches:           make(map[string]*fsWatch),
 		procs:             make(map[string]*processHandle),
@@ -131,7 +131,7 @@ func New(
 		nekoAuthClient:    nekoAuthClient,
 		policy:            &policy.Policy{},
 		eventStream:       eventStream,
-		captureSession:    captureSession,
+		telemetrySession:  telemetrySession,
 		cdpMonitor:        mon,
 		lifecycleCtx:      ctx,
 		lifecycleCancel:   cancel,
@@ -357,7 +357,7 @@ func (s *ApiService) Shutdown(ctx context.Context) error {
 	s.monitorMu.Lock()
 	s.lifecycleCancel()
 	s.cdpMonitor.Stop()
-	s.captureSession.Stop()
+	s.telemetrySession.Stop()
 	s.monitorMu.Unlock()
 	return s.recordManager.StopAll(ctx)
 }

server/cmd/api/api/api_test.go

@@ -11,8 +11,8 @@ import (
 
 	"log/slog"
 
-	"github.com/kernel/kernel-images/server/lib/capturesession"
 	"github.com/kernel/kernel-images/server/lib/devtoolsproxy"
+	"github.com/kernel/kernel-images/server/lib/telemetry"
 	"github.com/kernel/kernel-images/server/lib/events"
 	"github.com/kernel/kernel-images/server/lib/nekoclient"
 	oapi "github.com/kernel/kernel-images/server/lib/oapi"
@@ -305,20 +305,20 @@ func newMockNekoClient(t *testing.T) *nekoclient.AuthClient {
 	return client
 }
 
-func newCaptureSession(t *testing.T) (*capturesession.CaptureSession, *events.EventStream) {
+func newTelemetrySession(t *testing.T) (*telemetry.TelemetrySession, *events.EventStream) {
 	t.Helper()
 	es, err := events.NewEventStream(events.EventStreamConfig{RingCapacity: 64})
 	if err != nil {
 		t.Fatal(err)
 	}
-	return capturesession.NewCaptureSession(es), es
+	return telemetry.NewTelemetrySession(es), es
 }
 
-// newSvc constructs an ApiService with a fresh capture session and event stream.
+// newSvc constructs an ApiService with a fresh telemetry session and event stream.
 func newSvc(t *testing.T, mgr recorder.RecordManager) (*ApiService, error) {
 	t.Helper()
-	cs, es := newCaptureSession(t)
-	return New(mgr, newMockFactory(), newTestUpstreamManager(), scaletozero.NewNoopController(), newMockNekoClient(t), cs, es, 0)
+	ts, es := newTelemetrySession(t)
+	return New(mgr, newMockFactory(), newTestUpstreamManager(), scaletozero.NewNoopController(), newMockNekoClient(t), ts, es, 0)
 }
 
 func TestApiService_PatchChromiumFlags(t *testing.T) {