handler/session: add Validate() to catch nil Sessions and URLParamFunc at startup

[Copilot]

SessionHandler was the only handler in the package without a Validate() method, meaning nil Sessions or URLParamFunc fields caused a runtime panic instead of a startup error.

Changes

• handler/session.go — adds Validate() error following the established handler pattern; returns a descriptive error if Sessions or URLParamFunc is nil
• handler/session_test.go — adds three cases: nil Sessions, nil URLParamFunc, and a fully configured handler

func (h *SessionHandler) Validate() error {
    if h.Sessions == nil {
        return errors.New("SessionHandler misconfigured: Sessions is required")
    }
    if h.URLParamFunc == nil {
        return errors.New("SessionHandler misconfigured: URLParamFunc is required")
    }
    return nil
}

Greptile Summary

This PR adds a Validate() method to SessionHandler, catching nil Sessions and URLParamFunc fields at startup rather than allowing a nil-dereference panic at the first request. The implementation and error messages match the pattern used by every other handler in the package.

• handler/session.go: Validate() checks Sessions then URLParamFunc for nil, returning a descriptive error for each; no other logic is changed.
• handler/session_test.go: Three new test cases cover nil Sessions, nil URLParamFunc, and a fully configured handler, consistent with existing test style.

Confidence Score: 5/5

Safe to merge — the change is purely additive and touches no existing request-handling logic.

Both changed files are small and self-contained: a two-condition guard method and three matching tests. The implementation mirrors the pattern established by every other handler in the package, existing slog calls already pass context correctly, and no request paths are modified.

No files require special attention.

Important Files Changed

Filename	Overview
handler/session.go	Adds Validate() to SessionHandler following the established pattern; checks Sessions and URLParamFunc for nil with descriptive error messages. No issues found.
handler/session_test.go	Adds three focused test cases covering nil Sessions, nil URLParamFunc, and a fully configured handler. Tests are correct and consistent with the existing test style in the package.

Sequence Diagram

sequenceDiagram
    participant App as Application Startup
    participant SH as SessionHandler
    participant Store as SessionStore
    participant UPF as URLParamFunc

    App->>SH: Validate()
    SH->>Store: "Sessions == nil?"
    alt Sessions is nil
        SH-->>App: error: Sessions is required
    else Sessions is set
        SH->>UPF: "URLParamFunc == nil?"
        alt URLParamFunc is nil
            SH-->>App: error: URLParamFunc is required
        else URLParamFunc is set
            SH-->>App: nil (valid)
        end
    end

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Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0 new