fix(dexie-cloud): fix 'Illegal invocation' in blobResolveMiddleware cursor proxy

[liz709]

Problem

createBlobResolvingCursor() in blobResolveMiddleware wraps the IDB cursor via Object.create(cursor, { value, start }) but did not override key or primaryKey. Accessing these properties on the wrapped cursor falls through the prototype chain to the native IDBCursorWithValue getters, which require this to be the actual native IDB cursor object. Since this is a plain proxy object, the browser throws:

TypeError: Illegal invocation
    at IDBCursorWithValue.get [as key/primaryKey]
    at dexie-cloud-addon.js:...

Why does this happen? The observabilityMiddleware (level 0) only wraps cursors for secondary index queries — not primary key queries. For primary key queries, blobResolve (level 2) receives the cursor with no intermediate key/primaryKey getter override, so property lookup hits the native IDB getter directly.

This is a regression triggered by the level change in #2268 (moving blobResolve above the cache). At level -2 (below observability), blobResolve always received cursors already wrapped by observability. At level 2 (above observability), blobResolve can receive unwrapped native IDB cursors on primary key paths.

Fix

Add explicit key and primaryKey getters to the Object.create() property descriptor map. They close over the original cursor reference, matching the pattern used by Dexie's own ProxyCursor helper and the observabilityMiddleware/virtual-index-middleware:

key: {
  get() { return cursor.key; },
  enumerable: true,
},
primaryKey: {
  get() { return cursor.primaryKey; },
  enumerable: true,
},

What's NOT changed

• level: 2 is intentionally kept (set in Fix blob resolve issues (change level to be above cache-middleware) + make sure to resume blob downloader through syncComplete event #2268 so cached blob refs get resolved — reverting it would break cache invalidation for blob values).
• No behavioral change for value or start handling.

Testing

Build passes (pnpm build), unit tests pass (npm test in dexie-cloud-common), CodeRabbit: no findings.

Fixes: bug reported in Discord where app crashed on load with 'Illegal invocation' on dexie-cloud-addon 4.4.6–4.4.9 in Chrome on primary-key cursor queries.

Summary by CodeRabbit

• Bug Fixes
  • Fixed cursor operation errors that occurred in specific query contexts, resolving "Illegal invocation" TypeErrors during certain data retrieval operations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ec90f72f-c43e-4040-820d-094cec2955ca

📥 Commits

Reviewing files that changed from the base of the PR and between 2d92a26 and c52f589.

📒 Files selected for processing (1)

• addons/dexie-cloud/src/middlewares/blobResolveMiddleware.ts

---

📝 Walkthrough

Walkthrough

The createBlobResolvingCursor() function in the blob resolve middleware is updated to explicitly add key and primaryKey property accessors on the wrapped cursor. These accessors delegate to the underlying cursor, preventing prototype chain inheritance issues that cause "Illegal invocation" errors in specific query contexts.

Changes

Cohort / File(s)	Summary
Blob Cursor Wrapping addons/dexie-cloud/src/middlewares/blobResolveMiddleware.ts	Added explicit key and primaryKey property getters to the wrapped cursor object to override native IDBCursorWithValue prototype properties and avoid "Illegal invocation" TypeErrors when wrapping is otherwise unsafe.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• fix(dexie-cloud): WeakMap crash in DexieCloudDB + blob resolve middleware guard #2262: Modifies cursor-wrapping logic in the same middleware to handle cursor properties and lifecycle correctly.
• fix(blobResolveMiddleware): update wrappedCursor.value in non-blob and error paths #2275: Fixes related wrappedCursor issues in the same createBlobResolvingCursor implementation.

Suggested reviewers

• dfahlander

Poem

🐰 A cursor wrapped with care, so fine,
Its key and primaryKey in line,
No longer shall the prototype betray,
With explicit getters all the way! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately summarizes the main change: fixing an 'Illegal invocation' error in the blobResolveMiddleware cursor proxy, which is the primary objective of this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch liz/fix-blob-cursor-illegal-invocation

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[dfahlander]

Fixed and merged in #2293 (released in dexie-cloud-addon@4.4.10)