chore: stale FIXME comments on snapshot URL in execution-config defaults (already the real URL)

[teyrebaz33]

Summary

crates/execution-config/src/defaults.rs has two FIXME: Update this to the actual snapshot URL. comments attached to https://snapshots.arc.network/5042002:

// FIXME: Update this to the actual snapshot URL.
/// Default snapshot URL for Arc Network testnet (chain ID 5042002).
pub(crate) const DEFAULT_DOWNLOAD_URL: &str = "https://snapshots.arc.network/5042002";

and again a few lines later in init_download_urls() on the available_snapshots entry.

This is already the real, production snapshot URL, not a placeholder — confirmed two ways:

1. crates/snapshots/src/download.rs uses the same host with no such disclaimer:

   pub const SNAPSHOT_API_BASE_URL: &str = "https://snapshots.arc.network/api";

2. docs/running-an-arc-node.md documents https://snapshots.arc.network directly to users as the endpoint arc-snapshots fetches from, with no caveat about it being provisional.

Chain ID 5042002 also checks out independently as Arc Testnet (matches third-party RPC listings).

Why this is worth fixing

A stale FIXME reading 'update this to the actual URL' next to a URL that already is the actual URL is actively misleading — it invites a future contributor to 'fix' something that isn't broken, or to distrust a value that's already correct. Low severity, but it's a two-line removal once someone's looked into it.

Note

I only independently verified the testnet URL (5042002); didn't verify the devnet one (5042001) against an external source the way I did for testnet, so I'm not asserting that one's FIXME is stale by the same evidence — just flagging both exist textually. Happy to send the PR removing the FIXME(s) once confirmed.

[osr21]

Confirmed — this is a valid cleanup. Both FIXMEs in crates/execution-config/src/defaults.rs are stale; the URLs are already the real, working snapshot endpoints.

Where they are:

• L26 // FIXME: Update this to the actual snapshot URL. above DEFAULT_DOWNLOAD_URL = "https://snapshots.arc.network/5042002" (L28).
• L39 the same FIXME above the available_snapshots vec (L40 testnet …/5042002, L41 devnet …/5042001).
• DEFAULT_DOWNLOAD_URL / available_snapshots are referenced only within this file, so this is self-contained.

Evidence the URLs are real (not placeholders):

• GET https://snapshots.arc.network/5042002/latest.txt → 200, body:
  snapshot-arc-testnet-pruned-execution-20260821T0805Z-58103413.tar.lz4
  A live pointer to an actual pruned-execution testnet snapshot (block 58103413). The filename itself says arc-testnet, confirming 5042002 = Arc testnet.
• The domain root GET https://snapshots.arc.network/ → 200.

So the base URLs are correct and the FIXMEs no longer apply — safe to remove both.

One thing worth capturing so this doesn't regress: https://snapshots.arc.network/5042002 is a base/prefix, not a directly fetchable object. Curling the bare URL returns 404 (and deep keys like /latest or /snapshot.tar.gz return 400); only real object keys such as /latest.txt resolve. That's normal object-store behavior, but it's exactly the kind of thing that leads someone to curl the bare URL, see a 404, and re-add a "FIXME: fix this URL." When you strip the FIXMEs, consider replacing them with a one-liner like "base prefix; the pointer is <base>/latest.txt" to pre-empt that.

Devnet caveat (not a blocker): https://snapshots.arc.network/5042001/latest.txt currently returns 404 with body No snapshot available. The devnet endpoint is wired correctly — there's just no devnet snapshot published right now. That's an ops/data state, not a wrong URL, so it doesn't change the cleanup; just flagging in case a devnet snapshot is expected to exist.

Minor, adjacent nit: L40 bakes a label into the URL string — Cow::Borrowed("https://snapshots.arc.network/5042002 (testnet)"). It's harmless today because available_snapshots is display-only, but the (testnet) suffix makes it an invalid URL if anything ever consumes that vec as fetchable URLs. If the PR touches these lines anyway, splitting the label from the URL would be a cheap future-proofing.

Net: remove both FIXMEs; optionally add the "base prefix / latest.txt" note and split the label out of the L40 string.