Cloudflare Artifacts git push returns HTTP 500 at ~64 MiB pack

### What versions & operating system are you using?

```text
System:
OS: macOS 26.5
CPU: (10) arm64 Apple M1 Pro
Memory: 150.52 MB / 16.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Node: 25.9.0 - /opt/homebrew/bin/node
npm: 11.12.1 - /opt/homebrew/bin/npm
pnpm: 11.0.6 - /opt/homebrew/bin/pnpm
bun: 1.3.10 - /Users/noam/.bun/bin/bun
npmPackages:
miniflare: ^4.20260424.0 => 4.20260521.0
wrangler: ^4.93.0 => 4.94.0
```

Also observed with:

```text
git version 2.50.1 (Apple Git-155)
```

### Please provide a link to a minimal reproduction

https://github.com/noamt/cloudflare-artifacts-64m-repro

### Describe the Bug

### Summary

Pushing a fresh Git repository to a fresh Cloudflare Artifacts repo fails with raw HTTP 500 once the reachable Git pack is about 64 MiB.

This looks like a Cloudflare Artifacts pack-processing issue:
- Wrangler Artifacts commands successfully create repos and issue repo-scoped write tokens.
- Synthetic pushes succeed through 63 one-megabyte random binary files (local `size-pack: 63.02 MiB`).
- The same shape fails at 64 one-megabyte random binary files (local `size-pack: 64.03 MiB`).
- The Git client receives a raw HTTP 500 during `git push`; no structured Artifacts error code is surfaced.

### Reproduction steps

1. Clone the minimal repro repository:

```bash
git clone https://github.com/noamt/cloudflare-artifacts-64m-repro.git
cd cloudflare-artifacts-64m-repro
git gc --prune=now
git count-objects -vH
```

Observed local pack size:

```text
size-pack: 64.03 MiB
```

2. Create a fresh Cloudflare Artifacts repository and issue a write token:

```bash
npx wrangler artifacts repos create --namespace --default-branch main --json
npx wrangler artifacts repos issue-token --namespace --scope write --ttl 1800 --json
```

3. Push the repro commit to the returned Artifacts remote using the issued token:

```bash
git -c credential.helper= push --force HEAD:refs/heads/main
```

4. Optional comparison: generate the same synthetic repo with 63 files instead of 64. In my testing, the 63-file repo produced `size-pack: 63.02 MiB` and pushed successfully.

### Threshold observed

```text
1 MiB pack: 1.00 MiB -> push succeeds
4 MiB pack: 4.00 MiB -> push succeeds
8 MiB pack: 8.00 MiB -> push succeeds
16 MiB pack: 16.01 MiB -> push succeeds
24 MiB pack: 24.01 MiB -> push succeeds
32 MiB pack: 32.01 MiB -> push succeeds
48 MiB pack: 48.02 MiB -> push succeeds
52 MiB pack: 52.02 MiB -> push succeeds
56 MiB pack: 56.02 MiB -> push succeeds
60 MiB pack: 60.02 MiB -> push succeeds
62 MiB pack: 62.02 MiB -> push succeeds
63 MiB pack: 63.02 MiB -> push succeeds
64 MiB pack: 64.02/64.03 MiB -> HTTP 500 / send-pack disconnect
```

### Expected behavior

Artifacts should either accept this push or fail with a documented, structured limit/error. If there is a per-push, pack-size, request-body, or service-memory limit near 64 MiB, it would be useful for that limit to be documented and surfaced as a structured Artifacts error instead of a raw Git-side HTTP 500.

### Actual behavior

The Git push fails with HTTP 500 and disconnects during `send-pack`.

### Please provide any relevant error logs

```text
error: RPC failed; HTTP 500 curl 22 The requested URL returned error: 500
send-pack: unexpected disconnect while reading sideband packet
fatal: the remote end hung up unexpectedly
Everything up-to-date
```

Beginne mit dem Repository zur minimalen Reproduktion und führe git gc --prune=now sowie git count-objects -vH aus, um das ungefähr 64 MiB große Pack zu bestätigen. Erstelle mit Wrangler ein temporäres Artifacts-Repository, stelle ein Schreib-Token aus und vergleiche Pushes mit 63 MiB und 64 MiB. Abgeschlossen ist die Aufgabe, wenn der Push mit 64 MiB erfolgreich ist oder statt eines rohen HTTP 500 ein dokumentiertes, strukturiertes Limit zurückgibt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.