docs: restructure README to lead with Nix setup and improve flow

README.md

@@ -2,50 +2,15 @@
 
 Real-time mail delivery for maildirs via Fastmail's JMAP push API.
 
-Connects to Fastmail's JMAP EventSource stream and delivers new messages directly to a local Maildir the moment they arrive without polling.
+Connects to Fastmail's JMAP EventSource stream and delivers new messages directly to a local Maildir the moment they arrive without polling. On first run, or when saved JMAP state is stale, mbrts falls back to `mbsync` for a full sync, then takes over from that point.
 
-## How it works
+## Prerequisites
 
-On first run, or when the saved JMAP state is stale, mbrts falls back to `mbsync` for a full sync, then takes over from that point.
+Create a Fastmail API token at **Settings → Security → API Tokens**. This is distinct from an IMAP app password — mbrts requires a proper JMAP bearer token.
 
 ## Setup
 
-Create a Fastmail API token at **Settings → Security → API Tokens**.
-
-### Config file
-
-By default mbrts reads `$XDG_CONFIG_HOME/mbrts/config.yaml` (e.g. `~/.config/mbrts/config.yaml`):
-
-```yaml
-accounts:
-  - name: Personal
-    maildir_path: /home/you/.mail/Personal
-    password_command: "pass show fastmail/api-token"
-```
-
-Each account requires exactly one token source:
-
-| Field | Description |
-|---|---|
-| `password_command` | Shell command that prints the token to stdout |
-| `token_file` | Path to a file containing the token |
-| `token_env` | Name of an environment variable containing the token |
-
-Optional fields: `mbsync_account` (mbsync channel/group name; defaults to `name`), `log_level` (top-level: `debug`, `info`, `warn`, `error`).
-
-### CLI flags
-
-Every config file option has an equivalent flag. Flags override the config file. A single account can be configured entirely on the command line without a config file:
-
-```
-mbrts --name Personal \
-      --maildir-path ~/.mail/Personal \
-      --password-command "pass show fastmail/api-token"
-```
-
-Run `mbrts --help` for the full flag list, or `mbrts --version` to print the version.
-
-### Nix
+### Nix / home-manager
 
 Add mbrts as a flake input:
 
@@ -56,21 +21,11 @@ inputs.mbrts = {
 };
 ```
 
-The flake exposes:
-
-| Output | Description |
-|---|---|
-| `packages.*.default` | The `mbrts` binary |
-| `overlays.default` | Adds `pkgs.mbrts` |
-| `homeManagerModules.default` | The `services.mbrts` home-manager module |
-
-### home-manager module
-
-Add the overlay and module to your home-manager configuration, then configure the service:
+Add the overlay and module, then configure the service:
 
 ```nix
-# in your flake outputs
-overlays = [ inputs.mbrts.overlays.default ];
+# in your flake overlays
+inputs.mbrts.overlays.default
 
 # in your home-manager module list
 inputs.mbrts.homeManagerModules.default
@@ -88,23 +43,55 @@ services.mbrts = {
 };
 ```
 
-The module generates a config file and runs mbrts as a `systemd` user service. Logs are available via `journalctl --user -u mbrts -f`.
+The module generates a config file and runs mbrts as a systemd user service. Logs: `journalctl --user -u mbrts -f`.
 
-Module options:
+**Module options:**
 
 | Option | Type | Default | Description |
 |---|---|---|---|
 | `enable` | bool | — | Enable the service |
 | `package` | package | `pkgs.mbrts` | Package to use |
 | `logLevel` | enum | `"info"` | `debug`, `info`, `warn`, or `error` |
-| `accounts` | list | `[]` | List of account submodules (see config file fields above) |
+| `accounts` | list | `[]` | List of account submodules (see fields below) |
 
-## Build
+**Account fields** (each account requires exactly one token source):
+
+| Field | Description |
+|---|---|
+| `name` | Account name; used for state file and default mbsync channel |
+| `maildirPath` | Path to the local Maildir root |
+| `passwordCommand` | Shell command that prints the bearer token to stdout |
+| `tokenFile` | Path to a file containing the bearer token |
+| `tokenEnv` | Environment variable containing the bearer token |
+| `mbsyncAccount` | mbsync channel/group name for fallback (defaults to `name`) |
+
+### Standalone
+
+Build the binary:
 
 ```
 CGO_ENABLED=0 go build -o mbrts .
 ```
 
+By default mbrts reads `$XDG_CONFIG_HOME/mbrts/config.yaml` (e.g. `~/.config/mbrts/config.yaml`):
+
+```yaml
+accounts:
+  - name: Personal
+    maildir_path: /home/you/.mail/Personal
+    password_command: "pass show fastmail/api-token"
+```
+
+Every config file option has an equivalent CLI flag, and flags override the config file. A single account can be configured entirely on the command line:
+
+```
+mbrts --name Personal \
+      --maildir-path ~/.mail/Personal \
+      --password-command "pass show fastmail/api-token"
+```
+
+Run `mbrts --help` for the full flag list, or `mbrts --version` to print the version.
+
 ## aerc
 
 Configure the account source as `maildir://` so aerc picks up delivered messages immediately via inotify:
@@ -112,3 +99,70 @@ Configure the account source as `maildir://` so aerc picks up delivered messages
 ```ini
 source = maildir:///home/you/.mail/Personal
 ```
+
+## Using mbrts alongside mbsync
+
+mbrts handles inbound delivery; mbsync is still useful for pushing local changes (read flags, deletions, moves) back to Fastmail. They can coexist, but require careful configuration to avoid duplicate messages.
+
+**The problem:** mbsync tracks synced messages by IMAP UID in its own state database. It knows nothing about messages mbrts delivered directly to the Maildir. Because of this, mbsync re-downloads messages that mbrts has already written, creating duplicates.
+
+**The fix:** give mbsync two separate channels per account — one for the scheduled sync (flags and deletions only), and one for mbrts to call on-demand as a fallback when its JMAP state is missing or stale.
+
+```
+# scheduled channel — only pushes local changes upstream
+Channel Personal
+Far :Personal-remote:
+Near :Personal-local:
+Sync Flags Delete
+
+# pull channel — only used by mbrts on fallback
+Channel Personal-pull
+Far :Personal-remote:
+Near :Personal-local:
+Sync New
+```
+
+Point mbrts at the pull channel via `mbsync_account`:
+
+```yaml
+accounts:
+  - name: Personal
+    maildir_path: /home/you/.mail/Personal
+    password_command: "pass show fastmail/api-token"
+    mbsync_account: Personal-pull
+```
+
+Any scheduled mbsync timer then runs `mbsync Personal` (flags/deletions only), while mbrts calls `mbsync Personal-pull` on fallback (new messages only).
+
+### With home-manager
+
+Restrict the auto-generated channel to flags and deletions via `extraConfig.channel`, then append the pull-only channel via `programs.mbsync.extraConfig`:
+
+```nix
+# per-account: restrict scheduled sync to flags/deletions
+accounts.email.accounts.Personal.mbsync = {
+  enable = true;
+  extraConfig.channel.Sync = "Flags Delete";
+  # ... other mbsync options
+};
+
+# global: define a pull-only channel for mbrts fallback
+programs.mbsync.extraConfig = ''
+  Channel Personal-pull
+  Far :Personal-remote:
+  Near :Personal-local:
+  Sync New
+  Create Near
+  SyncState *
+'';
+
+# point mbrts at the pull channel
+services.mbrts.accounts = [
+  {
+    name = "Personal";
+    maildirPath = "/home/you/.mail/Personal";
+    passwordCommand = "pass show fastmail/api-token";
+    mbsyncAccount = "Personal-pull";
+  }
+];
+```