fix(transport): retry idempotent requests on network failures

[Andreas-Garcia]

A dropped browser↔Cloudflare connection (ERR_CONNECTION_CLOSED on grow staging) surfaced straight to the connectivity popup: React Query retry can't fire since fetchWrapper swallows the error via handleError.

fetchWrapper now retries GET/HEAD up to twice (300ms, 900ms) only when fetch throws. Error responses, aborted signals, and other methods are never retried.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🔵 Needs a closer look

It changes the retry/latency behavior of the core shared transport layer used by two production frontends, so a human should sign off on the operational trade-offs even though the implementation is clean and well-tested.

Review effort: Balanced
Findings: None

What changed in this PR

This PR hardens the shared transport layer so a dropped browser↔Cloudflare keep-alive connection (ERR_CONNECTION_CLOSED) no longer surfaces straight to the connectivity popup. Previously fetchWrapper swallowed the thrown fetch error via handleError, so React Query's own retry never got a chance to fire. The fix adds an internal, bounded retry around fetch for safe/idempotent methods only. This is a focused behavior change to @behindthemusictree/app-kit's transport module, which is consumed by both grow-the-music-tree-frontend and hear-the-music-tree-frontend.

Changes:

• Added fetchWithNetworkRetry that retries GET/HEAD up to twice (300ms, then 900ms) only when fetch itself throws, skipping aborted signals, error responses, and non-idempotent methods.
• Added tests covering recovery-after-retry, no-retry-for-POST/abort/error-response, and retry-exhaustion (3 total attempts), updating existing network-failure tests to drive fake timers.
• Added a CHANGELOG.md entry under [Unreleased] → Fixed.

File	Description
packages/​app-kit/​src/​transport/​fetch-wrapper.ts	Introduces bounded network retry for idempotent methods around the fetch call.
packages/​app-kit/​src/​transport/​fetch-wrapper.test.ts	Adds retry-behavior tests and adapts existing tests to fake timers.
CHANGELOG.md	Documents the retry behavior under [Unreleased].

---

💡 Configure MCP servers for context-aware, tailored reviews. Learn more in the docs.