[BUG] Claude.ai MCP servers only partially loaded in v2.1.104

Still broken in v2.1.104 (latest). Tagging @bcherny since the bot-driven duplicate chain has buried this.

Duplicate chain — all locked, none fixed:

• #40577 (my prior report) → closed as duplicate of #35939
• #35939 → closed as duplicate of #29730
• #29730 → closed for inactivity (stale) — the root issue was never actually fixed

Bug: With 10+ MCP servers configured in Claude.ai, only ~3 load per session. The rest are silently dropped — no error, no warning, no debug log entry. Root cause (per #35939): hardcoded batch concurrency of 3; servers not started before prompt processing begins are abandoned with no retry.

Steps to reproduce:

1. Configure 10+ MCP servers in Claude.ai
2. Launch Claude Code v2.1.104
3. Observe only 3 servers loaded despite all being discovered in --debug log

Expected: all configured servers load
Actual: only first batch of 3 loads, rest silently dropped

A pad-hack workaround exists (#29730) but there's no real fix. Please re-open or fix the underlying concurrency/batching logic.

Version: v2.1.104 | OS: macOS | Platform: Anthropic API