# S5: Archive checksum verification failure

Service harness, not a live update. The same runtime-driver.mjs invokes the real ServerSelfUpdate.make and pinned-runtime implementation from each checkout, with a synthetic HttpClient and a launcher that must never be called. Node v26.12.1 on Linux x64; no viewport or theme. Effect TestClock starts at 0 ms independently for each fixture.

Sequence on both sides, at virtual 0 ms: return HTTP 200 checksums containing an all-zero SHA-256; return HTTP 200 synthetic archive bytes; verify checksum and fail before extraction; observe cleanup and no handoff.

## Before

Revision: [4c361199f4](https://git.cafe/pingdotgg/t3code/commit/4c361199f47f6ea32a2c14835df392640d0f7c63)

```jsonl
{"virtualMs": 0, "event": "update-start", "targetVersion": "1.1.0", "clock": "Effect TestClock; starts at 0; real service implementation"}
{"virtualMs": 0, "event": "progress", "stage": "downloading"}
{"virtualMs": 0, "event": "request-start", "asset": "SHA256SUMS", "url": "https://github.com/pingdotgg/t3code/releases/download/v1.1.0/SHA256SUMS"}
{"virtualMs": 0, "event": "response-headers", "status": 200, "host": "github.com"}
{"virtualMs": 0, "event": "request-start", "asset": "archive", "url": "https://github.com/pingdotgg/t3code/releases/download/v1.1.0/t3-1.1.0-linux-x64.tar.gz"}
{"virtualMs": 0, "event": "response-headers", "status": 200, "host": "github.com"}
{"virtualMs": 0, "event": "update-failed", "reason": "Could not prepare t3@1.1.0.", "message": "Server update failed: Could not prepare t3@1.1.0.", "causeStep": "verifying the t3 release archive checksum"}
{"virtualMs": 0, "event": "cleanup-and-handoff", "stagingAndVersions": [], "processCalls": 0, "launcherCalls": 0}
```

## After

Revision: [53d9b7c289](https://git.cafe/pingdotgg/t3code/commit/53d9b7c2892601b6b9999f97f2db5b3cbf272746)

```jsonl
{"virtualMs": 0, "event": "update-start", "targetVersion": "1.1.0", "clock": "Effect TestClock; starts at 0; real service implementation"}
{"virtualMs": 0, "event": "progress", "stage": "downloading"}
{"virtualMs": 0, "event": "request-start", "asset": "SHA256SUMS", "url": "https://github.com/pingdotgg/t3code/releases/download/v1.1.0/SHA256SUMS"}
{"virtualMs": 0, "event": "response-headers", "status": 200, "host": "github.com"}
{"virtualMs": 0, "event": "request-start", "asset": "archive", "url": "https://github.com/pingdotgg/t3code/releases/download/v1.1.0/t3-1.1.0-linux-x64.tar.gz"}
{"virtualMs": 0, "event": "response-headers", "status": 200, "host": "github.com"}
{"virtualMs": 0, "event": "update-failed", "reason": "Could not prepare t3@1.1.0 while verifying the t3 release archive checksum.", "message": "Server update failed: Could not prepare t3@1.1.0 while verifying the t3 release archive checksum.", "causeStep": "verifying the t3 release archive checksum"}
{"virtualMs": 0, "event": "cleanup-and-handoff", "stagingAndVersions": [], "processCalls": 0, "launcherCalls": 0}
```

AI-assisted; verified with the tests and tools listed above.