fix: revert redis notifier watch change

[kx-byte]

Summary by Sourcery

Bug Fixes:

• Ensure the Redis notifier only delivers new messages by starting consumption from the special latest-message ID instead of an explicitly fetched last ID.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR simplifies Redis stream watching for MCP config updates by reverting a previous optimization and always starting the consumer from the latest message ID, ensuring Watch only delivers new updates after subscription begins.

Sequence diagram for RedisNotifier Watch starting from latest Redis stream message

sequenceDiagram
    actor WatchCaller
    participant RedisNotifier
    participant RedisClient
    participant RedisStream
    participant MCPConfigChannel

    WatchCaller->>RedisNotifier: Watch(ctx)
    activate RedisNotifier
    RedisNotifier->>RedisNotifier: create buffered channel (size 10)
    RedisNotifier->>RedisNotifier: start goroutine
    deactivate RedisNotifier

    par WatchLoop
        activate RedisNotifier
        RedisNotifier->>RedisNotifier: lastID = $
        loop read new messages
            RedisNotifier->>RedisClient: XRead from RedisStream starting at lastID
            RedisClient-->>RedisNotifier: new messages
            RedisNotifier->>MCPConfigChannel: push *MCPConfig
            RedisNotifier->>RedisNotifier: update lastID to latest message ID
        end
        deactivate RedisNotifier
    and ContextCancellation
        WatchCaller-->>RedisNotifier: ctx.Done()
        RedisNotifier->>MCPConfigChannel: close channel
    end

    MCPConfigChannel-->>WatchCaller: delivers only messages published after Watch started

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Class diagram for RedisNotifier Watch behavior change

classDiagram
    class RedisNotifier {
        - client RedisClient
        - streamName string
        + Watch(ctx Context) MCPConfigChannel
    }

    class RedisClient {
        + XRead(streamName string, lastID string) RedisMessages
    }

    class Context {
        + Done() DoneChannel
    }

    class MCPConfigChannel {
        + receive() MCPConfig
        + close()
    }

    class RedisMessages {
        + messages MCPConfig[*]
        + lastID string
    }

    class MCPConfig

    RedisNotifier --> RedisClient : uses
    RedisNotifier --> MCPConfigChannel : returns
    RedisNotifier --> Context : observes cancellation
    RedisClient --> RedisMessages : returns
    MCPConfigChannel --> MCPConfig : carries
    RedisMessages --> MCPConfig : contains

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File-Level Changes

Change	Details	Files
Redis notifier Watch now always starts consuming from the latest message ID instead of prefetching the current tail.	Removed pre-watch logic that queried Redis for the current stream tail using XRevRangeN and computed lastID based on the existing latest entry. Initialized lastID inside the Watch goroutine and set it to "$" so that XREAD starts from new messages only. Left the buffered channel creation and goroutine lifecycle (including deferred close on context cancellation) unchanged.	internal/mcp/storage/notifier/redis.go

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[sourcery-ai]

Hey - I've left some high level feedback:

• Switching lastID to $ means any messages published before Watch starts will be skipped; if this is intentional, consider expanding the comment to explicitly describe that we only deliver new updates and intentionally ignore historical ones so future readers don’t reintroduce the previous behavior.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Switching `lastID` to `$` means any messages published before `Watch` starts will be skipped; if this is intentional, consider expanding the comment to explicitly describe that we only deliver *new* updates and intentionally ignore historical ones so future readers don’t reintroduce the previous behavior.

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