feat(realtime): add multiple postgres_changes filters capability

capabilities/realtime.yaml

@@ -94,6 +94,10 @@ features:
     name: Postgres Changes Row Filter
     description: Apply a PostgREST-style filter expression (e.g. id=eq.200) to a Postgres changes subscription to receive events only for matching rows.
     group: subscriptions
+  - id: realtime.subscriptions.postgres_changes_multiple_filters
+    name: Multiple Postgres Changes Row Filters
+    description: Apply more than one PostgREST-style filter expression to a single Postgres changes subscription, combined with AND, to receive events only for rows matching all of them.
+    group: subscriptions
   - id: realtime.subscriptions.private_channel
     name: Private Channel (RLS)
     description: Mark a channel as private to enforce Row Level Security on Postgres change events and restrict broadcast and presence access to authorized users.

specs/realtime/subscriptions/postgres_changes_multiple_filters.md

@@ -0,0 +1,32 @@
+# Multiple Postgres Changes Row Filters
+
+## Behavior
+
+A single Postgres changes subscription accepts more than one PostgREST-style filter condition, combined with `AND`. Only rows matching every condition trigger an event.
+
+The conditions are expressed as one comma-separated filter string passed to the same `postgres_changes` binding — not as multiple separate subscriptions and not as an array field. For example, `id=eq.200,name=eq.foo` matches rows where `id` is `200` AND `name` is `foo`.
+
+This is a string-format capability, not a new wire message: the client passes the combined string through opaquely, and the Realtime server splits it on commas into individual `{column, operator, value, negate}` conditions before ANDing them into the underlying subscription query.
+
+Supported per-condition operators: `eq`, `neq`, `lt`, `lte`, `gt`, `gte`, `in`, `like`, `ilike`, `is`, `match`, `imatch`, `isdistinct`. Any operator can be negated with a `not.` prefix (e.g. `id=not.eq.5`).
+
+## Prerequisites
+
+Requires a Realtime server version that parses comma-delimited filter strings (older servers accept only a single condition per subscription).
+
+## Errors
+
+<!-- none named -->
+
+## Notes
+
+- Only `AND` semantics — there is no way to express `OR` across conditions within one filter string.
+- The `in` operator accepts at most 100 values.
+- Delete events cannot be filtered at all, regardless of filter count.
+- Values containing `,`, `(`, `)`, `"`, or `\` must be double-quoted so they aren't misread as a delimiter or operator boundary.
+- Unrelated to the `private` channel / RLS flag — combining filters works the same on public and private channels.
+
+## Related
+
+- [Postgres Changes Row Filter](realtime.subscriptions.postgres_changes_filter) — the single-filter form this extends
+- [Private Channel (RLS)](realtime.subscriptions.private_channel)