vMCP find_tool should have a dynamic description based on available tools

Problem

When using the vMCP optimizer, LLM agents often don't call find_tool because its generic description doesn't give them enough context about what tools are available behind it. Agents tend to reach for built-in tools (like bash, curl, or gh) instead, making it difficult to rely on the optimizer in practice.

This has been observed across multiple clients — Claude Code handles it best but still falls back to other approaches; Cursor and Copilot are significantly worse.

Proposed Solution

Allow the vMCP operator to manually configure a custom description for find_tool via OptimizerConfig. This description is global — all users see the same description regardless of their permissions.

For example, an operator could set the description to:

"Search for available tools. I have tools for accessing GitHub and Datadog."

This gives the LLM agent a hint about what capabilities are behind find_tool, making it far more likely to actually call it.

Solution sketch

1. Add FindToolDescription to OptimizerConfig (pkg/vmcp/config/config.go):

type OptimizerConfig struct {
    // ... existing fields ...

    // FindToolDescription overrides the default find_tool tool description.
    // Use this to hint at the kinds of tools available behind the optimizer
    // (e.g. "Search for tools. I have tools for GitHub, Datadog, and Slack.").
    // When empty, the built-in default description is used.
    // +optional
    FindToolDescription string `json:"findToolDescription,omitempty" yaml:"findToolDescription,omitempty"`
}

2. Pass the description through NewDecorator (pkg/vmcp/session/optimizerdec/decorator.go):

func NewDecorator(sess sessiontypes.MultiSession, opt optimizer.Optimizer, findToolDesc string) sessiontypes.MultiSession {
    if findToolDesc == "" {
        findToolDesc = defaultFindToolDescription
    }
    return &optimizerDecorator{
        MultiSession: sess,
        opt:          opt,
        optimizerTools: []vmcp.Tool{
            {
                Name:        FindToolName,
                Description: findToolDesc,
                InputSchema: findToolInputSchema,
            },
            // ... call_tool unchanged ...
        },
    }
}

3. Thread it through the factory (pkg/vmcp/server/sessionmanager/factory.go):

The optimizerDecoratorFn already has access to the config. Pass OptimizerConfig.FindToolDescription into NewDecorator at line 190.

Future improvements (out of scope)

• Per-permission dynamic descriptions (e.g. if a user has access to tool set X, concatenate a relevant hint to the base description)
• LLM-generated summaries that automatically describe available tools based on the indexed backends

Start with pkg/vmcp/config/config.go and inspect OptimizerConfig, then trace NewDecorator in pkg/vmcp/session/optimizerdec/decorator.go and the optimizerDecoratorFn in pkg/vmcp/server/sessionmanager/factory.go. Add the optional description flow so configured text is used for find_tool while the built-in default remains effective when empty.