https://gitlab.synchro.net/main/sbbs/-/issues/941#note_8997

Audited the Wildcat! 4 macro reference (System Information, User Record Information, Connection variables, Screen control codes, Color codes — from the `Wildcat-4.pdf` manual) against the Synchronet sources (`atcodes.cpp` value-codes and `putmsg.cpp` display-control codes).

The large majority of Wildcat! `@`-codes are already supported under the same name (`@BBS@`, `@USER@`, `@PHONE@`, `@CLS@`, `@PAUSE@`, `@NOSTOP@`, `@STOP@`, `@NOCODE@`, `@PROTOCOL@`, the `@DOWNK@`/`@UPK@`/`@KBLEFT@`/`@MAXDL@` family, etc.).

### Aliases added (`atcodes.cpp`) — codes that already existed under a different name

| Wildcat! code | Synchronet code |
|---|---|
| `@ACCBAL@` | `@CREDITS@` |
| `@USERID@` | `@USERNUM@` |
| `@CALLID@` | `@CID@` |
| `@CONNECT@` | `@CONN@` |
| `@ID@` | `@QWKID@` |
| `@ENTER@` | `@PAUSE@` (approximate — Wildcat! waits for Enter, Synchronet's pause is hit-any-key) |

(Builds clean; commit pending review.)

### Genuinely missing — no equivalent
- `@CONFOP@` — sub-board operator name
- `@INCHAT@` — number of users active in chat
- `@MAXRATIO@` — maximum download ratio
- `@NETBAL@` — netmail balance

### Not applicable to Synchronet's model
- `@FAX@` — no fax field in the user record
- `@MODEM@` — modem name from MDM file (telnet-era / N/A)
- `@YNDEF@` — per-language default Yes/No characters (handled differently)
- `@ELSE@` / `@ENDIF@` / `@IFSEC [sec]@` — Wildcat!'s IF/ELSE/ENDIF block model; Synchronet uses `@SHOW:@` for conditional display instead
- `@NOPREV@` — no previous-page toggle in Synchronet's pause model

Color codes (`@BF@` hex background/foreground format) are a separate topic from the @-codes above; Synchronet's `@XON@`/`@XOFF@` already toggle PCBoard/Wildcat-style color-code interpretation.
--- SBBSecho 3.37-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

https://gitlab.synchro.net/main/sbbs/-/issues/941#note_9000

Follow-up: implemented `@IFSEC=ars@` / `@ELSE@` / `@ENDIF@` conditional display blocks (commit 60a19b084), so these are no longer "N/A".

Rather than Wildcat!'s named security profiles, the argument is a Synchronet **Access Requirement String** (e.g. `SYSOP`, `LEVEL40`, `FLAG1A`); both `@IFSEC=ars@` and `@IFSEC:ars@` are accepted. Implemented in `putmsgfrag` alongside the other Wildcat! display-control codes, reusing the same output-suppression flag as `@SHOW@`/`@SYSONLY@`.

Differences from Wildcat!:
- The codes may appear anywhere in a line (not only column 0) and share a line with other text/codes.
- Blocks do not nest (same restriction Wildcat! documents).

Verified live against a level-50 reader. Documented at https://wiki.synchro.net/custom:atcodes#conditional_display_ifsec

Still genuinely missing (no equivalent): `@CONFOP@`, `@INCHAT@`, `@MAXRATIO@`, `@NETBAL@`.
--- SBBSecho 3.37-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)