Explain the SSL failure instead of just reporting it

A Postgres URL without an sslmode made lib/pq ask for TLS and die with
"SSL is not enabled on the server", which reads like a server fault when
it is really a connection-string default. The error now says what to
append, and the server retries briefly so a deploy is not marked
unhealthy just because Postgres was still starting.

The sync server URL also defaults to the hosted instance now, so a fresh
install needs no setup.

AGENTS.md

@@ -40,11 +40,16 @@ clicking an item copies it back to the clipboard.
   a global queue); only the store append hops back to main.
 - `Sources/Prompt/SyncService.swift` — optional sync client. Holds the group
   code and server URL in `UserDefaults` (`sync.code`, `sync.serverURL`,
-  `sync.version`), pushes the whole store as JSON, and polls every 5s.
+  `sync.version`). The URL defaults to `SyncService.defaultServerURL`
+  (`https://prompt.tzgyn.dev`); nothing is sent anywhere until a code exists,
+  because polling only runs when one is set. Pushes the whole store as JSON and
+  polls every 5s.
 - `Server/main.go` — the Go sync backend (single file, `net/http` + `lib/pq`).
-  Also ships `Server/README.md` (self-hosting) and `Server/prompt-sync.service`
-  (systemd unit). Logs one line per request, creates its schema on startup, and
-  shuts down gracefully on SIGTERM so a redeploy cannot cut off a push.
+  Also ships `Server/Dockerfile` (static binary on distroless) and
+  `Server/README.md` (self-hosting). Logs one line per request, creates its
+  schema on startup, shuts down gracefully on SIGTERM so a redeploy cannot cut
+  off a push, and supports `-healthcheck` (pings local `/healthz`) so the
+  shell-less image needs no curl for its Docker `HEALTHCHECK`.
 
 ## Sync protocol
 

README.md

@@ -58,15 +58,20 @@ PROMPT_SYNC_DATABASE_URL="postgres://localhost:5432/prompt_sync?sslmode=disable"
   go run .          # listens on :8080
 ```
 
-Then in the panel: click the sync icon, set the server URL (e.g.
-`http://192.168.1.10:8080` or an HTTPS host), and either **Generate Code** on
-the first Mac or paste the code into **Join** on the other.
+Or build the Docker image (`docker build -t prompt-sync Server/`) and point it
+at your own Postgres — see [Server/README.md](Server/README.md) for that and for
+deploying to a host.
+
+Then in the panel: click the sync icon (or Cmd+,), confirm the server URL, and
+either **Generate Code** on the first Mac or paste the code into **Join** on the
+other.
 
 Notes:
 
-- Both Macs must be able to reach the server. A LAN address or a Tailscale
-  hostname works; `localhost` only works if the server runs on the same Mac.
-  See [Server/README.md](Server/README.md) to deploy it on a VPS or home server.
+- Sync defaults to `https://prompt.tzgyn.dev`; change it in the sync panel to
+  point at your own server. Both Macs must be able to reach it — a LAN address
+  or a Tailscale hostname works, and `localhost` only works if the server runs
+  on the same Mac. See [Server/README.md](Server/README.md) to deploy it.
 - Joining a group that already has notes replaces what's on that Mac.
 - The app polls every 5 seconds (a tiny version check) and pushes 1.5s after a
   change; last write wins, and changes that came from the server are not echoed

Server/.dockerignore

@@ -0,0 +1,4 @@
+.git
+prompt-sync
+prompt-sync-*
+*.md

Server/Dockerfile

@@ -0,0 +1,27 @@
+# Build stage: the server is pure Go (lib/pq is pure Go), so CGO is off and the
+# result is a static binary that runs on a shell-less base image.
+FROM golang:1.26-alpine AS build
+
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY *.go ./
+
+ARG TARGETOS
+ARG TARGETARCH
+RUN CGO_ENABLED=0 GOOS=${TARGETOS:-linux} GOARCH=${TARGETARCH} \
+    go build -trimpath -ldflags="-s -w" -o /prompt-sync .
+
+# Runtime stage: distroless has no shell, so the binary does its own
+# healthcheck (see -healthcheck in main.go). Runs as non-root.
+FROM gcr.io/distroless/static-debian12:nonroot
+
+COPY --from=build /prompt-sync /prompt-sync
+
+ENV PROMPT_SYNC_ADDR=:8080
+EXPOSE 8080
+
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD ["/prompt-sync", "-healthcheck"]
+
+ENTRYPOINT ["/prompt-sync"]

Server/README.md

@@ -26,21 +26,68 @@ PROMPT_SYNC_DATABASE_URL="postgres://localhost:5432/prompt_sync?sslmode=disable"
 
 The schema is created on startup. Every request is logged as
 `METHOD PATH STATUS DURATION`; SIGTERM/SIGINT shut down gracefully so an
-in-flight push is not cut off mid-write.
+in-flight push is not cut off mid-write. If the database is not reachable yet
+it retries five times, 2s apart, before giving up.
 
-## Deploy to a Linux host
+> **`sslmode` matters.** lib/pq defaults to `sslmode=require`, so a connection
+> string copied from a host that runs Postgres *without* TLS (Coolify's
+> internal Postgres, a plain `docker run postgres`, Homebrew) fails with
+> `pq: SSL is not enabled on the server`. Append `?sslmode=disable` in that
+> case — the server prints exactly that hint when it hits this.
+
+## Deploying with Coolify
+
+Use a Dockerfile application pointed at this repo with base directory `Server/`
+(so Coolify builds `Server/Dockerfile`), expose port `8080`, and set:
+
+| Variable | Value |
+| --- | --- |
+| `PROMPT_SYNC_DATABASE_URL` | your Postgres URL **plus `?sslmode=disable`** |
+| `PROMPT_SYNC_ADDR` | `:8080` (this is already the default) |
+
+Coolify detects the `HEALTHCHECK` in the Dockerfile and runs
+`prompt-sync -healthcheck` with its 5s start period, so the container only goes
+live once `/healthz` answers. It also logs a generic warning that a healthcheck
+needs `curl` or `wget` — that does not apply here, the binary does its own
+check, so there is no reason to add either to the image (it is distroless and
+has no shell).
+
+## Run with Docker
+
+The image is a static binary on `distroless` (non-root, no shell), so its
+`HEALTHCHECK` calls `prompt-sync -healthcheck`, which pings the local
+`/healthz` — no curl needed in the image. That is what `docker ps` reports as
+the container health.
 
 ```bash
-# from the repo root, on the Mac
-cd Server
-GOOS=linux GOARCH=arm64 go build -o prompt-sync .    # amd64 for x86 hosts
-scp prompt-sync <host>:/tmp/ && ssh <host> 'sudo mv /tmp/prompt-sync /usr/local/bin/'
+docker build -t prompt-sync Server/
+docker run -d --name prompt-sync -p 8080:8080 \
+  -e PROMPT_SYNC_DATABASE_URL="postgres://user:pass@host:5432/prompt_sync?sslmode=disable" \
+  prompt-sync
 
-# on the host: create the database and role, then
-sudo cp Server/prompt-sync.service /etc/systemd/system/
-sudo systemctl edit --full prompt-sync   # set PROMPT_SYNC_DATABASE_URL
-sudo systemctl enable --now prompt-sync
-journalctl -u prompt-sync -f             # verify it is listening
+docker logs -f prompt-sync         # request log
+```
+
+Postgres stays outside the container; the server only needs a URL. If Postgres
+runs on the Docker host itself, `host` is `host.docker.internal` on macOS and
+Windows, or the host's LAN address on Linux (`--network host` also works).
+
+## Deploy to a host
+
+Build for the host's architecture and ship the image, or build it on the host
+itself (a `git clone` plus `docker build` is usually simplest):
+
+```bash
+# build on the Mac for a linux/arm64 host, then copy it over
+docker build --platform linux/arm64 -t prompt-sync Server/
+docker save prompt-sync | gzip > prompt-sync.tar.gz
+scp prompt-sync.tar.gz <host>:
+ssh <host> 'gunzip -c prompt-sync.tar.gz | docker load'
+
+ssh <host> 'docker run -d --name prompt-sync --restart unless-stopped \
+  -p 8080:8080 \
+  -e PROMPT_SYNC_DATABASE_URL="postgres://user:pass@db-host:5432/prompt_sync?sslmode=disable" \
+  prompt-sync'
 ```
 
 Put it behind TLS if it is reachable from the internet — the code is the only

Server/main.go

@@ -27,6 +27,7 @@ import (
 	"os"
 	"os/signal"
 	"regexp"
+	"strings"
 	"syscall"
 	"time"
 
@@ -48,6 +49,13 @@ type Server struct {
 }
 
 func main() {
+	// -healthcheck pings the local /healthz and exits non-zero on failure. It
+	// exists so the container image can run on a shell-less base (distroless),
+	// where there is no wget or curl for a HEALTHCHECK to use.
+	if len(os.Args) > 1 && os.Args[1] == "-healthcheck" {
+		os.Exit(healthcheck())
+	}
+
 	dsn := os.Getenv("PROMPT_SYNC_DATABASE_URL")
 	if dsn == "" {
 		dsn = "postgres://localhost:5432/prompt_sync?sslmode=disable"
@@ -57,14 +65,11 @@ func main() {
 		addr = ":8080"
 	}
 
-	db, err := sql.Open("postgres", dsn)
+	db, err := openDatabase(dsn)
 	if err != nil {
-		log.Fatalf("open database: %v", err)
+		log.Fatalf("connect to database: %v%s", err, hintFor(err))
 	}
 	defer db.Close()
-	if err := db.Ping(); err != nil {
-		log.Fatalf("connect to database: %v", err)
-	}
 	if _, err := db.Exec(schema); err != nil {
 		log.Fatalf("ensure schema: %v", err)
 	}
@@ -103,6 +108,63 @@ func main() {
 	}
 }
 
+// openDatabase connects, retrying briefly so a deploy is not marked unhealthy
+// just because Postgres was still starting up.
+func openDatabase(dsn string) (*sql.DB, error) {
+	db, err := sql.Open("postgres", dsn)
+	if err != nil {
+		return nil, err
+	}
+	var lastErr error
+	for attempt := 1; attempt <= 5; attempt++ {
+		if lastErr = db.Ping(); lastErr == nil {
+			return db, nil
+		}
+		if attempt < 5 {
+			log.Printf("database not ready (attempt %d/5): %v", attempt, lastErr)
+			time.Sleep(2 * time.Second)
+		}
+	}
+	db.Close()
+	return nil, lastErr
+}
+
+// hintFor turns the most common connection failure into something actionable.
+// lib/pq defaults to sslmode=require, so any DSN copied from a host that runs
+// Postgres without TLS (Coolify's internal Postgres, docker-compose, Homebrew)
+// fails with a bare "SSL is not enabled on the server".
+func hintFor(err error) string {
+	if !strings.Contains(err.Error(), "SSL is not enabled") {
+		return ""
+	}
+	return "\n\nhint: lib/pq defaults to sslmode=require, but that Postgres has TLS off." +
+		"\n      Append ?sslmode=disable to PROMPT_SYNC_DATABASE_URL" +
+		"\n      (e.g. postgres://user:pass@host:5432/prompt_sync?sslmode=disable)."
+}
+
+// healthcheck returns 0 when the local /healthz answers 200.
+func healthcheck() int {
+	addr := os.Getenv("PROMPT_SYNC_ADDR")
+	if addr == "" {
+		addr = ":8080"
+	}
+	if strings.HasPrefix(addr, ":") {
+		addr = "127.0.0.1" + addr
+	}
+	client := &http.Client{Timeout: 3 * time.Second}
+	response, err := client.Get("http://" + addr + "/healthz")
+	if err != nil {
+		log.Printf("healthcheck: %v", err)
+		return 1
+	}
+	defer response.Body.Close()
+	if response.StatusCode != http.StatusOK {
+		log.Printf("healthcheck: unexpected status %d", response.StatusCode)
+		return 1
+	}
+	return 0
+}
+
 // withLogging keeps a one-line trail of method, path, status and duration so a
 // self-hosted deployment can be debugged from journalctl or docker logs.
 func withLogging(next http.Handler) http.Handler {

Server/prompt-sync.service

@@ -1,22 +0,0 @@
-[Unit]
-Description=Prompt sync server
-Documentation=https://gitea.tzgyn.dev/TZGyn/prompt
-After=network-online.target postgresql.service
-Wants=network-online.target
-
-[Service]
-# The binary is built on a Mac with:
-#   GOOS=linux GOARCH=arm64 go build -o prompt-sync .
-ExecStart=/usr/local/bin/prompt-sync
-Environment=PROMPT_SYNC_ADDR=:8080
-Environment=PROMPT_SYNC_DATABASE_URL=postgres://prompt:CHANGE_ME@localhost:5432/prompt_sync?sslmode=disable
-Restart=on-failure
-RestartSec=2
-# The server only needs to talk to Postgres and bind :8080.
-NoNewPrivileges=true
-PrivateTmp=true
-ProtectSystem=strict
-ProtectHome=true
-
-[Install]
-WantedBy=multi-user.target

Sources/Prompt/SyncService.swift

@@ -39,6 +39,9 @@ final class SyncService: ObservableObject {
     private static let urlKey = "sync.serverURL"
     private static let versionKey = "sync.version"
 
+    /// Where sync points unless the user overrides it in the sync panel.
+    static let defaultServerURL = "https://prompt.tzgyn.dev"
+
     private var lastVersion: Int64 {
         get { Int64(defaults.integer(forKey: Self.versionKey)) }
         set { defaults.set(newValue, forKey: Self.versionKey) }
@@ -54,7 +57,7 @@ final class SyncService: ObservableObject {
 
     private init() {
         code = defaults.string(forKey: Self.codeKey)
-        serverURL = defaults.string(forKey: Self.urlKey) ?? "http://localhost:8080"
+        serverURL = defaults.string(forKey: Self.urlKey) ?? Self.defaultServerURL
     }
 
     func start() {