How Paste Switch solved macOS input position tracking for clipboard overlays

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Developer of Paste Switch, a macOS clipboard utility, faced a complex challenge in positioning a small overlay near the active text cursor when cycling through clipboard items. macOS does not expose a uniform accessibility interface across native apps, browsers, and Electron apps, meaning the same caret-position API can return exact coordinates, element-level frames, or nothing at all. The solution uses Apple's Accessibility API starting with AXSelectedTextRange and AXBoundsForRange, but falls back to element frame data when precise caret bounds are unavailable. A decision tree with detailed logging distinguishes between exact caret positions and approximate input-box anchors, preventing the overlay from appearing on the wrong monitor or at a stale location. The approach highlights how seemingly minor UI details in utility apps can require significant engineering to handle edge cases across different application surfaces.

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React 19 useCallback Stale Closures Can Leak Tenant Data in Multi-Tenant Apps

A developer shipping a multi-tenant AI dashboard discovered that React 19's useCallback memoization can cause stale closures that leak one tenant's data into another tenant's API calls. The bug surfaced in production when rapid tenant switches occurred while async AI requests were still in-flight, resulting in Tenant B's Claude API calls inadvertently using Tenant A's system prompts. Although the dependency array correctly lists tenantId, it only guards against stale values at render time and cannot cancel or correct closures already captured during ongoing async operations. The issue is particularly hard to catch because it leaves no TypeScript errors, no failed requests, and no visible staging-environment symptoms. In SaaS applications, this silent timing flaw constitutes a data isolation violation that can affect hundreds of tenant accounts concurrently.

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ProgrammingDEV Community ·

Tutorial: Build a Local Services Flutter App Using HosteDay Backend Platform

A new developer tutorial demonstrates how to build a local services app called 'At Your Service' using Flutter and the HosteDay backend platform. The guide walks through creating a free backend server on HosteDay, setting up a database table for service providers, and auto-generating CRUD API endpoints without writing manual backend code. Developers then create a Flutter project in Android Studio and integrate the hosteday_flutter package to connect the app to the backend. API token protection is configured within the Flutter project to secure backend requests from unauthorized access. This first part of the series lays the foundation for future authentication and service-listing features.

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ProgrammingDEV Community ·

How HTTP/2 Multiplexing Replaced Multiple Connections with One Efficient Link

HTTP/1.1 handled growing web traffic by opening multiple TCP connections simultaneously, which improved page load speeds but created significant overhead in handshakes, memory, and CPU usage. Engineers identified that the core issue was not network capacity but how HTTP utilized the network. HTTP/2 was developed to address this by introducing multiplexing, which allows multiple requests and responses to travel concurrently over a single TCP connection as independent streams. The protocol breaks data into smaller units called frames, which can be interleaved across streams and reassembled correctly by the browser. HTTP/2 also shifted from a text-based format to binary, making it more efficient for computers to process.

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ProgrammingDEV Community ·

Guide: Migrating Python Projects from mypy to ty and Pyrefly

A practical migration guide documents how the fastkml Python package was moved from mypy to Astral's ty and Meta's pyrefly type checkers. The guide recommends running both tools simultaneously, as they each catch different subsets of type errors that the other may miss. Before making any changes, developers are advised to establish a baseline error count and categorize issues by error kind to identify systemic root causes rather than fixing problems file by file. The guide also warns that mypy configuration flags do not map one-to-one to ty or pyrefly equivalents, urging developers to re-derive intent rather than hunt for identical settings. Finally, it stresses verifying that both tools pass cleanly alongside a full test suite before retiring the existing mypy configuration.

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