feat(phase-16): anonymous play & share telemetry substrate (wave 16.1)

Player-service play-session tracker (floor + 3-bucket classify), SharePopover share tracker with debounce, sendBeacon interop, proxied rate-limited POST api/event/{play,share}, append-only event logs + incremental play_counter with server-side release resolution. Migration authored, not applied. No anonId, no read surface.

DeepDrftAPI/Controllers/EventController.cs

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+using DeepDrftData;
+using DeepDrftModels.DTOs;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.RateLimiting;
+
+namespace DeepDrftAPI.Controllers;
+
+/// <summary>
+/// Anonymous play/share telemetry intake (Phase 16 §2.2 / §4.3). Unauthenticated — same posture as the
+/// public reads — but IP rate-limited (the "events" limiter, registered in Program.cs) and payload-
+/// validated to make casual inflation annoying (§2.5). Both endpoints return <c>202 Accepted</c>: these
+/// are fire-and-forget telemetry, not transactions, and the client (a <c>sendBeacon</c>) never reads the
+/// response. The release dimension on a play is resolved server-side from the track key (§2.3 / D4).
+/// The controller is a thin HTTP boundary; all write logic lives in <see cref="IEventService"/>.
+/// </summary>
+[ApiController]
+[Route("api/event")]
+[EnableRateLimiting("events")]
+public class EventController : ControllerBase
+{
+    // Reject oversized bodies before deserialization — a coarse abuse guard (§2.5). The legitimate
+    // payloads are a track key + an enum, well under 1 KB.
+    private const int MaxBodyBytes = 1024;
+
+    private readonly IEventService _eventService;
+    private readonly ILogger<EventController> _logger;
+
+    public EventController(IEventService eventService, ILogger<EventController> logger)
+    {
+        _eventService = eventService;
+        _logger = logger;
+    }
+
+    // POST api/event/play (unauthenticated, rate-limited)
+    [HttpPost("play")]
+    [RequestSizeLimit(MaxBodyBytes)]
+    public async Task<ActionResult> RecordPlay([FromBody] PlayEventDto payload, CancellationToken ct = default)
+    {
+        // Reject a missing track key and an out-of-range bucket (§2.5). [ApiController] model binding
+        // already 400s a malformed/oversized body and an undefined enum value, but the explicit guards
+        // keep the contract obvious and cover the empty-string key the model binder lets through.
+        if (string.IsNullOrWhiteSpace(payload.TrackEntryKey))
+            return BadRequest("trackEntryKey is required");
+        if (!Enum.IsDefined(payload.Bucket))
+            return BadRequest("bucket is invalid");
+
+        // Wave 16.1 writes no anonId — defend the substrate by dropping any the client sends early.
+        var result = await _eventService.RecordPlay(payload.TrackEntryKey, payload.Bucket, anonId: null, ct);
+        if (!result.Success)
+        {
+            // A telemetry failure must never surface to the listener as an error they can act on, but
+            // we still log it and answer 5xx so a monitor can see the substrate is unhealthy. The
+            // beacon ignores the status either way.
+            _logger.LogWarning("RecordPlay failed: {Error}", result.Messages.FirstOrDefault()?.Message);
+            return StatusCode(500);
+        }
+
+        return Accepted();
+    }
+
+    // POST api/event/share (unauthenticated, rate-limited)
+    [HttpPost("share")]
+    [RequestSizeLimit(MaxBodyBytes)]
+    public async Task<ActionResult> RecordShare([FromBody] ShareEventDto payload, CancellationToken ct = default)
+    {
+        if (string.IsNullOrWhiteSpace(payload.TargetKey))
+            return BadRequest("targetKey is required");
+        if (!Enum.IsDefined(payload.TargetType))
+            return BadRequest("targetType is invalid");
+        if (!Enum.IsDefined(payload.Channel))
+            return BadRequest("channel is invalid");
+
+        var result = await _eventService.RecordShare(payload.TargetType, payload.TargetKey, payload.Channel, anonId: null, ct);
+        if (!result.Success)
+        {
+            _logger.LogWarning("RecordShare failed: {Error}", result.Messages.FirstOrDefault()?.Message);
+            return StatusCode(500);
+        }
+
+        return Accepted();
+    }
+}