fix(usage): route usage readings through the assigned connection proxy

[maxmad64bis]

⚠️ base-red inherited: #15306

Summary

Quota reads leave the server directly even when the connection has a proxy assigned, because the dispatcher doesn't pass the connection id down to the readers. The nine covered readers now send their vendor requests through the assigned proxy, while connections without one keep the same direct reads.

Related Issues

• Related to fix(quota): route quota fetcher reads through the connection proxy #15885
• Related to fix(quota): route remaining console quota reads through the connection proxy #16344

Target Branch

• Base is the active release/v3.8.x branch (the highest open release/v*), not main
• New feature? From 3.8.55 on it is held with the v4-feature label for the v4 channel

Validation

• Change type: provider
• Focused tests and category gates from the golden path
• npm run lint
• Reconciled with the current active release base; focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR

Tests Added Or Updated

• tests/unit/usage-connection-proxy.test.ts — conol reads through an assigned proxy, unchanged direct reads without one, proxied failure surfacing as the existing message, and a static guard that fails on any reintroduced bare fetch.

Coverage Notes

• open-sse/services/usage.ts — tests/unit/usage-connection-proxy.test.ts (conol path through the dispatcher).
• open-sse/services/connectionProxyFetch.ts — tests/unit/usage-connection-proxy.test.ts (proxy, no-proxy, and failure cases).
• open-sse/services/conolUsage.ts — tests/unit/usage-connection-proxy.test.ts (proxy, direct, and failure cases).
• open-sse/services/usage/github.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/claude.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/codex.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/cursor.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/syntx.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/devinCli.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/chatplayground.ts — tests/unit/usage-connection-proxy.test.ts (static guard).
• open-sse/services/usage/command-code.ts — tests/unit/usage-connection-proxy.test.ts (static guard).

Reviewer Notes

• Behavior: reads from connections with an assigned proxy now go out through that proxy; reads without one are unchanged.
• Merge: after fix(quota): route quota fetcher reads through the connection proxy #15885 and after fix(quota): route remaining console quota reads through the connection proxy #16344 — they share the helper file only.
• Follow-up: the ~25 direct fetches left outside these readers, including the claude bootstrap fetch, move to a follow-up change.