relay message file upload cannot succeed: the file is never uploaded

[khaliqgant]

relay message file upload cannot succeed. The file is never uploaded — the CLI serialises the local path into the attachments array and the server rejects it.

Reproduce

relay agent register upload-probe          # capture the token
RELAY_AGENT_TOKEN=$TOK relay channel create probe-ch
printf 'hello\n' > /tmp/probe.txt
RELAY_AGENT_TOKEN=$TOK relay message file upload /tmp/probe.txt --channel probe-ch --text 'x'
# Invalid attachments: file ids must exist in workspace and be complete

Verified against production cloud with a clean fixture, a fresh agent and a fresh channel.

Root cause

packages/cli/src/cli/commands/message.ts sends:

attachments: [{ type: 'file', path: filePath }]

serializeAttachmentInputs (packages/sdk/src/messaging/relaycast-translate.ts:301) is just:

typeof attachment === 'string' ? attachment : JSON.stringify(attachment)

so the literal string {"type":"file","path":"/tmp/probe.txt"} is sent where the API expects a file id. Nothing ever reads the file or uploads bytes.

What the API actually requires

@relaycast/types file.d.ts defines a three-step presigned upload:

1. POST UploadRequest { filename, content_type, size_bytes } → UploadResponse { id, upload_url, expires_at }
2. PUT the bytes to upload_url
3. Send the message with attachments: [file_id]; the record must reach status: "complete"

@relaycast/sdk exposes no files API (relay.d.ts has no files/upload member), so this needs SDK support before the CLI can be fixed.

Secondary bug

--help documents --text as defaulting to "", but the API rejects empty text with text is required — so the documented default can never work. Either make --text required or default it to the filename.

Impact

message-file-upload is verify_tier: 3 in the feature manifest — presented as a supported feature that cannot work at all.

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Found by workflows/verify-features.ts during a live end-to-end run.