add snapshot patch routes

[breardon2011]

Snapshot patch API — adds POST/GET/DELETE /snapshots/:name/patches so you can attach patches to snapshots by name instead of having to know the
underlying checkpoint ID. Resolves snapshot → checkpoint internally, delegates to existing patch logic. No new tables or migrations.

Snapshot "my-env" → checkpoint cp-A
├── Sandbox sb-1 (based_on_checkpoint_id = cp-A, last_patch_sequence = 0)
│ └── Checkpoint cp-B (sb-1's frozen state)
│ └── Sandbox sb-3 (based_on_checkpoint_id = cp-B, last_patch_sequence = 0)
└── Sandbox sb-2 (based_on_checkpoint_id = cp-A, last_patch_sequence = 0)

You add a patch to snapshot "my-env" (which patches cp-A):

• sb-1: gets the patch on next wake (based on cp-A)
• sb-2: gets the patch on next wake (based on cp-A)
• cp-B: does NOT get patched — it's a frozen artifact, not a running sandbox
• sb-3: does NOT get the patch — it's based on cp-B, not cp-A

Patches are one level deep. They apply to sandboxes whose based_on_checkpoint_id matches the patched checkpoint. That's it. No cascading through
checkpoint chains.

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Project	Deployment	Actions	Updated (UTC)
opensandbox	Ready	Preview, Comment	Mar 28, 2026 1:26am

[breardon2011]

Going to do a follow up PR on the way the SDK handles returning "creating" and "running" etc, so there is something more awaitable, and errors are surfaced from patching more cleanly