Feat/supabase subscriber

[vani-rf]

Add Supabase Realtime as a second Pub/Sub provider, enabling subscribers to listen to real-time database changes, broadcast messages, and presence events via WebSocket (Phoenix Channels protocol).

This PR refactors the pubsub architecture from Google-only to multi-provider, then adds the Supabase Realtime provider on top.

What changed

Architecture (commit 74e743d):

• Refactored PubSubManager to use map-based provider registry (map[PubSubProviderType]PubSubProvider)
• Extracted Google provider to pkg/pubsub/google/ (no circular dependency)
• Added provider-agnostic SubscriberMessage wrapper
• Added WrapLegacySubscriber for backward compatibility

Supabase Realtime Provider (commit c1ad763):

• New pkg/pubsub/supabase/provider.go — WebSocket client with Phoenix channels protocol, 30s heartbeat, exponential backoff reconnect
• Supports all 3 channel types: Broadcast, Presence, Postgres Changes
• Added ChannelType(), Table(), Schema(), EventFilter() to SubscriberHandler interface with non-breaking defaults in SubscriberBase
• Added RealtimeEventFilter string constants in pkg/supabase/constants (RealtimeEventAll, RealtimeEventInsert, RealtimeEventUpdate, RealtimeEventDelete)
• Reuses existing config (SupabasePublicUrl, AnonKey, ServiceKey) — no new env vars
• Root adapter (SupabaseRealtimeProvider) maps Realtime messages to SubscriberMessage

Type of change

• New feature (non-breaking change which adds functionality)
• Unit Tests

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Commands Run

golangci-lint run # clean
go vet ./... # clean
go test ./... # all pass
go test -cover ./pkg/pubsub/supabase/ # 86.3% coverage

Further comments

• Non-breaking: Adding methods to SubscriberHandler is safe because all subscribers must embed SubscriberBase (required for code generation detection), which provides defaults.
• No new env vars: Supabase Realtime derives WebSocket URL from SupabasePublicUrl and authenticates with ServiceKey/AnonKey.
• OpenSpec spec updated with 3 new requirements (Supabase Realtime, Postgres Changes Filtering, SubscriberBase Code Gen Detection). Change proposal archived.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 68 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/pubsub/supabase/provider.go	81.95%	27 Missing and 8 partials ⚠️
pubsub.go	84.57%	27 Missing and 6 partials ⚠️

Flag	Coverage Δ
go-1.22	73.58% <83.33%> (+0.53%)	⬆️
go-1.24	72.89% <83.33%> (+0.62%)	⬆️
go-1.25	72.87% <83.33%> (+0.67%)	⬆️
macos-latest	73.38% <83.33%> (+0.31%)	⬆️
ubuntu-latest	73.66% <83.33%> (+0.60%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
pubsub.go	83.58% <84.57%> (+34.01%)	⬆️
pkg/pubsub/supabase/provider.go	81.95% <81.95%> (ø)

... and 1 file with indirect coverage changes

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