[vansh (vansh-nagar)]

Pull Request

📖 Description

A FAST element with a connection-aware injected property keeps its initial dependency after moving to a DOM container that provides a different instance. The reconnection callback resolves the new instance but writes the old captured value back into the cache.

Cache the newly resolved value before notifying subscribers. The regression moves a real custom element through different containers and back, checks what subscribers read during notification, checks that a move between containers providing the same instance emits no notification, and preserves the respectConnection: false behavior.

🎫 Issues

Fixes #7743

👩‍💻 Reviewer Notes

Implementation and tests were developed with Codex. The production fix is a single assignment; the test runs against actual DOM lifecycle callbacks.

📑 Test Plan

• Before the fix (Chromium): respectConnection=true fails because the property and notifications still contain the initial value; the false control passes.
• After the fix: both cases pass in Chromium, Firefox, and WebKit (6/6).
• npm exec -w @microsoft/fast-element -- playwright test src/di/ --retries=0 --workers=4: all 825 dependency-injection cases pass across the three browsers.
• npm run build: eight successful monorepo builds and one cached/skipped task, no failures (macOS arm64, Node 26.0.0).
• npm test: 12 successful monorepo tasks, two cached/skipped tasks, no failures. The source suite has 4,604 passes and seven skips; all 618 declarative cases and 138 harness browser cases pass across Chromium, Firefox, and WebKit.
• npm run format:check, npm run checkchange, and npm run test:validation pass.
• Biome checks pass with five pre-existing unused-variable/private-member warnings.

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

Agents

• I have linked to an existing issue in this project that this change addresses
• I have read the skills
• I have read the DESIGN.md file(s) in packages relevant to my changes
• I have updated the DESIGN.md file(s) in packages relevant to my changes

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