[cttq] fix: When create redis_conn,check if connection already exists

[warning128]

修复当使用redis 作为 session_conn时,发送事件Queue与处理事件的conn不一致的问题
Fixes #267

Summary by Sourcery

Reuse existing Redis session connections in RedisStore.Get and renew TTL for sessions and ID sets to fix inconsistent session connections when using Redis for sessions.

Bug Fixes:

• Reuse existing Redis session connections when available to prevent mismatched event queue and processing connections.

Enhancements:

• Renew TTL for session data and the session ID set when reusing a connection to keep sessions active.

[sourcery-ai]

Reviewer's Guide

Adds a pre-fetch check in RedisStore.Get to reuse existing connections from the active connections map and renew their TTLs, ensuring consistent session usage without recreating connections each time.

Sequence diagram for RedisStore.Get connection reuse and TTL renewal

sequenceDiagram
participant "Caller"
participant "RedisStore"
participant "RedisClient"
participant "Logger"

"Caller"->>"RedisStore": Get(ctx, id)
activate "RedisStore"
"RedisStore"->>"RedisStore": Check connections[id]
alt Connection exists
    "RedisStore"->>"RedisClient": Expire(key, ttl)
    "RedisClient"-->>"RedisStore": (result)
    alt Expire error
        "RedisStore"->>"Logger": Warn("failed to renew session TTL")
    end
    "RedisStore"->>"RedisClient": Expire(prefix+"ids", ttl)
    "RedisClient"-->>"RedisStore": (result)
    alt Expire error
        "RedisStore"->>"Logger": Warn("failed to renew session ID set TTL")
    end
    "RedisStore"-->>"Caller": conn
else Connection does not exist
    "RedisStore"->>"RedisClient": Get(key)
    "RedisClient"-->>"RedisStore": data
    ... (rest of original logic)
end

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File-Level Changes

Change	Details	Files
Reuse existing Redis session connections	Acquire read lock on connections map Check for existing connection by session ID Renew TTL for session key and session ID set Return existing connection early Release read lock after the check	internal/mcp/session/redis.go

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#267	Fix the bug where, with SESSION_STORAGE_TYPE=redis, redis_conn does not receive Queue messages after establishing a long HTTP_GET connection.	✅
#267	Ensure that when tools/call fails, the long connection in redis_conn receives error_message events, matching the behavior of memory session storage.	✅
#267	Prevent creation of a new redis connection for each session if one already exists, so that event sending and handling use the same connection.	✅

Possibly linked issues

• [BUG] 在配置SESSION_STORAGE_TYPE=redis时, 在HTTP_GET建立长连接后, redis_conn收不到Queue消息 #267: The PR fixes the issue by reusing existing Redis connections instead of creating new ones, resolving message reception failure.

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• Consider using defer to release the read lock right after acquiring it to simplify control flow and prevent accidental double-unlock.
• Extract the TTL renewal calls into a helper method to reduce duplication and centralize session expiration logic.
• Ensure expired connections are removed from s.connections elsewhere to prevent stale entries and potential memory leaks.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider using defer to release the read lock right after acquiring it to simplify control flow and prevent accidental double-unlock.
- Extract the TTL renewal calls into a helper method to reduce duplication and centralize session expiration logic.
- Ensure expired connections are removed from s.connections elsewhere to prevent stale entries and potential memory leaks.

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