feat(messages): add --send-at flag to messages send (cueapi #623 parity)

[mikemolinet]

Summary

Adds optional --send-at flag to cueapi messages send for per-message scheduling. Server-side support landed in cueapi #623.

Behavior

• Omitted: message delivered immediately (existing behavior).
• ISO 8601 timestamp: server stores send_at on the message row and the worker picks it up when due.
• Past timestamp: treated as 'send now' (idempotent — no error).

Implementation

send_at flows as a body field on /v1/messages. Verified via app/schemas/message.py MessageCreate schema (cueapi #623). Same-day SDK ports already shipped: cueapi-python PR #34, cueapi-mcp manifest #31 references.

Tests

Extended test_messages_send_help_lists_required_flags to pin --send-at in help output. 184/184 tests pass.

Source

Drift audit handoff/cueapi-package-drift-2026-05-06. Backlog row "Parity port: PR #623 → cueapi-cli" (p1). cueapi-main confirmed cueapi-cli lane mine via [CC-CUEAPI-CLI-LANE-OPTION-B-YOURS].

🤖 Generated with Claude Code

[mikemolinet]

Superseded by cueapi-cli #49 (merged 2026-05-10, a9151b1) which added --send-at to messages send along with --notify and --mode parity flags. Main's send-at implementation is fuller (better help text + composed with BCC-light + Surface 6 mode hint) than this PR's. Closing — no re-port needed.

For future me: this PR sat for 4 days on a stale base while my afternoon attention was elsewhere; the messages send_at port was completed via the broader #49 PR which composed multiple related primitives. Lesson: when sibling PRs touch the same command surface, the larger composed PR wins and the older split-out PR becomes stale fast.