refactor(server): deduplicate session ID extraction into a shared helper

[Copilot]

The three-line pattern for extracting a session ID from X-Agent-ID/Authorization headers was copy-pasted in two places in the same package. Because this is security-sensitive (session tracking divergence between logging and validation is a real risk), the duplication is worth eliminating.

Changes

• internal/server/session.go — adds a package-private helper:

  func extractSessionIDFromRequest(r *http.Request) string {
      return auth.ExtractSessionIDFromHeaders(
          r.Header.Get("X-Agent-ID"),
          r.Header.Get("Authorization"),
      )
  }

• session.go (extractAndValidateSession) and middleware.go (WithSDKLogging) — each inline 3-line block replaced with a single call to the new helper.

No behaviour change; header precedence logic remains in auth.ExtractSessionIDFromHeaders.

[Copilot]

Pull request overview

This PR refactors the internal/server package to eliminate duplicated session ID extraction logic by introducing a single shared helper that reads X-Agent-ID / Authorization from an *http.Request and delegates precedence/validation to auth.ExtractSessionIDFromHeaders.

Changes:

• Added a package-private extractSessionIDFromRequest(*http.Request) string helper in internal/server/session.go.
• Updated extractAndValidateSession to use the new helper instead of an inline 3-line header extraction block.
• Updated WithSDKLogging middleware to use the same helper for consistent session ID extraction in logging.

Show a summary per file

File	Description
internal/server/session.go	Adds extractSessionIDFromRequest and uses it from extractAndValidateSession to centralize header-based session ID extraction.
internal/server/middleware.go	Switches WithSDKLogging to call extractSessionIDFromRequest to keep logging/session extraction consistent with validation.

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• Files reviewed: 2/2 changed files
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