Strip shell session env vars from BuildDescription signature.

OLDPWD and TERM_SESSION_ID change across terminal/shell sessions but
don't affect build output. Including them in the signature can
invalidate the on-disk BuildDescription cache for cosmetic differences,
producing redundant bundle directories per terminal session.

Author: rjmansfield

Sources/SWBTaskExecution/BuildDescriptionSignature.swift

@@ -57,7 +57,7 @@ package struct BuildDescriptionSignatureComponents: Codable, Hashable, Sendable
     let targets: [TargetMetadata]
     let projects: [ProjectMetadata]
     let systemInfo: SystemInfo?
-    let userInfo: UserInfo?
+    var userInfo: UserInfo?
     let developerPath: Path
     let xcodeVersionString: String
     let xcodeProductBuildVersionString: String
@@ -106,10 +106,31 @@ package struct BuildDescriptionSignatureComponents: Codable, Hashable, Sendable
     }
 }
 
+extension BuildDescriptionSignatureComponents {
+    /// Env vars stripped from `UserInfo` before hashing into the signature.
+    /// These change across terminal/shell sessions but don't affect build output
+    /// and including them can invalidate the on-disk cache for cosmetic differences.
+    fileprivate static let environmentDenylist: Set<String> = [
+        "OLDPWD",
+        "TERM_SESSION_ID",
+    ]
+
+    fileprivate static func filteredEnvironmentForSignature(_ env: [String: String]) -> [String: String] {
+        env.filter { !environmentDenylist.contains($0.key) }
+    }
+}
+
 extension BuildDescriptionSignatureComponents {
     var humanReadableString: ByteString {
         get throws {
-            try ByteString(JSONEncoder(outputFormatting: [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes]).encode(self))
+            var components = self
+            if let ui = components.userInfo {
+                components.userInfo = UserInfo(
+                    user: ui.user, group: ui.group, uid: ui.uid, gid: ui.gid, home: ui.home,
+                    processEnvironment: Self.filteredEnvironmentForSignature(ui.processEnvironment),
+                    buildSystemEnvironment: Self.filteredEnvironmentForSignature(ui.buildSystemEnvironment))
+            }
+            return try ByteString(JSONEncoder(outputFormatting: [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes]).encode(components))
         }
     }