HyperFile P1 privileged-helper XPC peer validation

Resolved the P1 helper peer-validation gap in an isolated HyperFile worktree: the helper now checks each incoming connection's process code signature against the expected HyperFile client requirement before exposing the privileged XPC interface.

Scope

• Host: rdmsm4x only.
• Canonical checkout: /Users/richh/dev/apps/hyperFile remained clean on main at 9a6490008de329427f6a335840a7e0d44ae59b96.
• Isolated worktree: /Users/richh/dev/_worktrees/hyperfile-p1-xpc-peer-validation-20260828.
• Branch and commit: codex/hyperfile-p1-xpc-peer-validation-20260828 at 0964612a8fc8647b87e573dd8d1dd6abce84b11d.

Changes

• Added Helper/HelperPeerValidation.swift, which resolves the incoming NSXPCConnection.processIdentifier with SecCodeCopyGuestWithAttributes(kSecGuestAttributePid:), compiles the one shared client requirement, and calls SecCodeCheckValidity.
• Updated Helper/main.swift so ServiceDelegate rejects a connection before exporting the privileged protocol or calling resume() when validation fails.
• Added the macOS HyperFileHelperPeerValidationTests Xcode test target and its one focused rejection test.
• Regenerated HyperFile.xcodeproj/project.pbxproj from project.yml and verified the validation source is compiled only by the helper and test targets, not by either app target.
• Updated STATUS.md, ISSUES.md, INTERFACES.md, and FEATURE_MATRIX.md to record P1 and the test-target finding as resolved while preserving all other open items.

Verification

• xcodebuild -project HyperFile.xcodeproj -scheme HyperFileHelperPeerValidationTests -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO test — 1 test, 0 failures.
• xcodebuild -project HyperFile.xcodeproj -scheme HyperFile-macOS -configuration Debug -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO build — BUILD SUCCEEDED.
• xcodebuild -project HyperFile.xcodeproj -scheme com.eastcoastscience.HyperFile.Helper -configuration Debug -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO build — BUILD SUCCEEDED.
• xcodegen generate --use-cache preserved the project file hash, and git diff --check was clean before commit.

Explicitly not performed

• No canonical-main merge or push.
• No code signing, helper registration/installation, launch, deployment, entitlement changes, iOS work, MCP work, or credential use.

Undo / rollback

• Preserve the branch/worktree for review. If this commit is later integrated and needs reversal, revert 0964612a8fc8647b87e573dd8d1dd6abce84b11d in the integration branch.
• If the isolated worktree is no longer needed after review, remove it with git -C /Users/richh/dev/apps/hyperFile worktree remove /Users/richh/dev/_worktrees/hyperfile-p1-xpc-peer-validation-20260828; this does not affect canonical main.

Outstanding owner actions

• Review and integrate the isolated commit when appropriate. P2/P3 items in ISSUES.md remain untouched.