WhatsApp: add group and direct system prompt support (#59553)

Merged via squash.

Prepared head SHA: 63e2b50e01
Co-authored-by: Bluetegu <1525690+Bluetegu@users.noreply.github.com>
Co-authored-by: omarshahine <10343873+omarshahine@users.noreply.github.com>
Reviewed-by: @omarshahine

docs/channels/groups.md

@@ -408,6 +408,10 @@ The agent system prompt includes a group intro on the first turn of a new group
 - List chats: `imsg chats --limit 20`.
 - Group replies always go back to the same `chat_id`.
 
+## WhatsApp system prompts
+
+See [WhatsApp](/channels/whatsapp#system-prompts) for the canonical WhatsApp system prompt rules, including group and direct prompt resolution, wildcard behavior, and account override semantics.
+
 ## WhatsApp specifics
 
 See [Group messages](/channels/group-messages) for WhatsApp-only behavior (history injection, mention handling details).

docs/channels/whatsapp.md

@@ -465,6 +465,75 @@ Behavior notes:
   </Accordion>
 </AccordionGroup>
 
+## System prompts
+
+WhatsApp supports Telegram-style system prompts for groups and direct chats via the `groups` and `direct` maps.
+
+Resolution hierarchy for group messages:
+
+The effective `groups` map is determined first: if the account defines its own `groups`, it fully replaces the root `groups` map (no deep merge). Prompt lookup then runs on the resulting single map:
+
+1. **Group-specific system prompt** (`groups["<groupId>"].systemPrompt`): used if the specific group entry defines a `systemPrompt`.
+2. **Group wildcard system prompt** (`groups["*"].systemPrompt`): used when the specific group entry is absent or defines no `systemPrompt`.
+
+Resolution hierarchy for direct messages:
+
+The effective `direct` map is determined first: if the account defines its own `direct`, it fully replaces the root `direct` map (no deep merge). Prompt lookup then runs on the resulting single map:
+
+1. **Direct-specific system prompt** (`direct["<peerId>"].systemPrompt`): used if the specific peer entry defines a `systemPrompt`.
+2. **Direct wildcard system prompt** (`direct["*"].systemPrompt`): used when the specific peer entry is absent or defines no `systemPrompt`.
+
+Note: `dms` remains the lightweight per-DM history override bucket (`dms.<id>.historyLimit`); prompt overrides live under `direct`.
+
+**Difference from Telegram multi-account behavior:** In Telegram, root `groups` is intentionally suppressed for all accounts in a multi-account setup — even accounts that define no `groups` of their own — to prevent a bot from receiving group messages for groups it does not belong to. WhatsApp does not apply this guard: root `groups` and root `direct` are always inherited by accounts that define no account-level override, regardless of how many accounts are configured. In a multi-account WhatsApp setup, if you want per-account group or direct prompts, define the full map under each account explicitly rather than relying on root-level defaults.
+
+Important behavior:
+
+- `channels.whatsapp.groups` is both a per-group config map and the chat-level group allowlist. At either the root or account scope, `groups["*"]` means "all groups are admitted" for that scope.
+- Only add a wildcard group `systemPrompt` when you already want that scope to admit all groups. If you still want only a fixed set of group IDs to be eligible, do not use `groups["*"]` for the prompt default. Instead, repeat the prompt on each explicitly allowlisted group entry.
+- Group admission and sender authorization are separate checks. `groups["*"]` widens the set of groups that can reach group handling, but it does not by itself authorize every sender in those groups. Sender access is still controlled separately by `channels.whatsapp.groupPolicy` and `channels.whatsapp.groupAllowFrom`.
+- `channels.whatsapp.direct` does not have the same side effect for DMs. `direct["*"]` only provides a default direct-chat config after a DM is already admitted by `dmPolicy` plus `allowFrom` or pairing-store rules.
+
+Example:
+
+```json5
+{
+  channels: {
+    whatsapp: {
+      groups: {
+        // Use only if all groups should be admitted at the root scope.
+        // Applies to all accounts that do not define their own groups map.
+        "*": { systemPrompt: "Default prompt for all groups." },
+      },
+      direct: {
+        // Applies to all accounts that do not define their own direct map.
+        "*": { systemPrompt: "Default prompt for all direct chats." },
+      },
+      accounts: {
+        work: {
+          groups: {
+            // This account defines its own groups, so root groups are fully
+            // replaced. To keep a wildcard, define "*" explicitly here too.
+            "120363406415684625@g.us": {
+              requireMention: false,
+              systemPrompt: "Focus on project management.",
+            },
+            // Use only if all groups should be admitted in this account.
+            "*": { systemPrompt: "Default prompt for work groups." },
+          },
+          direct: {
+            // This account defines its own direct map, so root direct entries are
+            // fully replaced. To keep a wildcard, define "*" explicitly here too.
+            "+15551234567": { systemPrompt: "Prompt for a specific work direct chat." },
+            "*": { systemPrompt: "Default prompt for work direct chats." },
+          },
+        },
+      },
+    },
+  },
+}
+```
+
 ## Configuration reference pointers
 
 Primary reference:
@@ -478,6 +547,7 @@ High-signal WhatsApp fields:
 - multi-account: `accounts.<id>.enabled`, `accounts.<id>.authDir`, account-level overrides
 - operations: `configWrites`, `debounceMs`, `web.enabled`, `web.heartbeatSeconds`, `web.reconnect.*`
 - session behavior: `session.dmScope`, `historyLimit`, `dmHistoryLimit`, `dms.<id>.historyLimit`
+- prompts: `groups.<id>.systemPrompt`, `groups["*"].systemPrompt`, `direct.<id>.systemPrompt`, `direct["*"].systemPrompt`
 
 ## Related