From fe1c3a95e060c77a30ff4767c171fdc8bd5ccc10 Mon Sep 17 00:00:00 2001
From: Kyle Barron <kyle@developmentseed.org>
Date: Mon, 11 May 2026 16:23:37 -0400
Subject: [PATCH] wip: Debugging spurious zarrita cancellation errors in
 aef-mosaic example

---
 examples/aef-mosaic/src/aef/get-tile-data.ts |  24 +++-
 examples/aef-mosaic/src/main.tsx             | 123 +++++++++++++++++++
 2 files changed, 146 insertions(+), 1 deletion(-)

diff --git a/examples/aef-mosaic/src/aef/get-tile-data.ts b/examples/aef-mosaic/src/aef/get-tile-data.ts
index 60bd7a62..bbbfd4fd 100644
--- a/examples/aef-mosaic/src/aef/get-tile-data.ts
+++ b/examples/aef-mosaic/src/aef/get-tile-data.ts
@@ -25,7 +25,29 @@ export async function getTileData(
 ): Promise<AefTileData> {
   const { device, sliceSpec, width, height, signal } = options;
 
-  const chunk = await zarr.get(arr, sliceSpec, { signal });
+  // TEMP DIAGNOSTIC
+  const sigTag =
+    signal && (signal as AbortSignal & { __id?: string }).__id !== undefined
+      ? (signal as AbortSignal & { __id: string }).__id
+      : signal
+        ? "sig#?"
+        : "<none>";
+  console.log(
+    `[diag] getTileData enter x=${options.x} y=${options.y} z=${options.z} sig=${sigTag} aborted=${signal?.aborted ?? "<none>"}`,
+  );
+
+  const chunk = await zarr.get(arr, sliceSpec, { signal }).catch((err) => {
+    console.log(
+      `[diag] zarr.get threw for x=${options.x} y=${options.y} z=${options.z}`,
+      {
+        sig: sigTag,
+        signalAborted: signal?.aborted,
+        signalReason: signal?.reason,
+        err,
+      },
+    );
+    throw err;
+  });
   const { data } = chunk;
 
   // Shape after slicing must be [NUM_BANDS, height, width]. The `time` dim
diff --git a/examples/aef-mosaic/src/main.tsx b/examples/aef-mosaic/src/main.tsx
index f6350f9b..1d6e627c 100644
--- a/examples/aef-mosaic/src/main.tsx
+++ b/examples/aef-mosaic/src/main.tsx
@@ -1,7 +1,130 @@
+import { _Tile2DHeader } from "@deck.gl/geo-layers";
 import { StrictMode } from "react";
 import { createRoot } from "react-dom/client";
 import App from "./App.js";
 
+// TEMP DIAGNOSTIC — track every change to `_isCancelled` and every onError
+// call so we can pinpoint why AbortError reaches onTileError.
+{
+  type TileState = Record<string, unknown> & {
+    id?: string;
+    __cancelTrace?: string[];
+  };
+  const proto = _Tile2DHeader.prototype as unknown as {
+    abort: (this: TileState) => void;
+    _loadData: (
+      this: TileState,
+      opts: { onError: (err: unknown, tile: unknown) => void },
+    ) => Promise<void>;
+  };
+
+  // Replace _isCancelled with a getter/setter that records every write into
+  // an in-memory ring buffer per tile (prev->value with a label, no stack
+  // capture so we don't tank perf during fast pans).
+  const STORE = "__cancelStore";
+  let activeLabel = "init";
+  const labeled = <T,>(label: string, fn: () => T): T => {
+    const prev = activeLabel;
+    activeLabel = label;
+    try {
+      return fn();
+    } finally {
+      activeLabel = prev;
+    }
+  };
+  Object.defineProperty(_Tile2DHeader.prototype, "_isCancelled", {
+    configurable: true,
+    get(this: TileState) {
+      return (this as Record<string, unknown>)[STORE] as boolean;
+    },
+    set(this: TileState, value: boolean) {
+      const prev = (this as Record<string, unknown>)[STORE];
+      (this as Record<string, unknown>)[STORE] = value;
+      if (!this.__cancelTrace) {
+        this.__cancelTrace = [];
+      }
+      this.__cancelTrace.push(`${prev}->${value} @ ${activeLabel}`);
+      if (this.__cancelTrace.length > 30) {
+        this.__cancelTrace.shift();
+      }
+    },
+  });
+
+  const origAbort = proto.abort;
+  proto.abort = function patchedAbort(this: TileState) {
+    return labeled(`abort#${this.id}`, () => origAbort.call(this));
+  };
+
+  // Assign a stable id to each AbortSignal created so we can tell whose
+  // signal is whose.
+  let nextSignalId = 0;
+  const idFor = (
+    signal: (AbortSignal & { __id?: string }) | null | undefined,
+  ): string => {
+    if (!signal) {
+      return "<none>";
+    }
+    if (signal.__id === undefined) {
+      Object.defineProperty(signal, "__id", {
+        value: `sig#${nextSignalId++}`,
+        enumerable: false,
+      });
+    }
+    return signal.__id as string;
+  };
+
+  // Patch AbortController to give each new signal an id at construction.
+  const OrigController = window.AbortController;
+  class TaggedController extends OrigController {
+    constructor() {
+      super();
+      idFor(this.signal);
+    }
+  }
+  window.AbortController = TaggedController;
+
+  // Patch AbortController.prototype.abort to log every call regardless of
+  // caller (tile.abort, or anything else).
+  const origCtrlAbort = OrigController.prototype.abort;
+  OrigController.prototype.abort = function patchedCtrlAbort(
+    this: AbortController,
+    reason?: unknown,
+  ) {
+    console.warn("[diag] controller.abort()", {
+      sig: idFor(this.signal),
+      activeLabel,
+      stack: new Error().stack?.split("\n").slice(2, 6).join(" | "),
+    });
+    return origCtrlAbort.call(this, reason);
+  };
+
+  const origLoadData = proto._loadData;
+  proto._loadData = async function patchedLoadData(
+    this: TileState,
+    opts: { onError: (err: unknown, tile: unknown) => void },
+  ) {
+    const myLoaderId = this._loaderId;
+    const tag = `[diag] _loadData#${myLoaderId} ${this.id}`;
+    const wrappedOnError = (err: unknown, tile: unknown) => {
+      const ctrl = this._abortController as AbortController | null;
+      console.warn(`${tag} onError FIRED`, {
+        err,
+        ownSignal: idFor(ctrl?.signal),
+        ownSignalAborted: ctrl?.signal.aborted,
+        ownSignalReason: ctrl?.signal.reason,
+        cancelTrace: this.__cancelTrace?.slice(),
+        contentNull: this.content === null,
+        currentLoaderId: this._loaderId,
+        myLoaderId,
+      });
+      return opts.onError(err, tile);
+    };
+    return labeled(`loadData#${myLoaderId}/${this.id}`, () =>
+      origLoadData.call(this, { ...opts, onError: wrappedOnError }),
+    );
+  };
+}
+
 createRoot(document.getElementById("root")!).render(
   <StrictMode>
     <App />