refactor(filesystem): preserve admitted file facts

Return the validated descriptor and its original metadata from regular-file
admission. Propagate that contract through owned reads, hashes, snapshots,
artifact inventory and provider file workflows instead of replacing initial
facts with another stat. Keep arbitrary output-handle operations separate.

Preserve final descriptor/path identity proofs, borrowed-source verification,
BigInt precision, cancellation provenance and failed-close ownership. Remove
the obsolete source and owned-ZIP baseline stages and update their consumers
and regressions. Tie read completion faults to actual reads instead of the
retired duplicate stat; instrument real handles without fake handle wrappers.

Validation: fresh runtime/catalog build; focused source, lifecycle, filesystem,
CLI/MCP and authored provider-fixture tests; full static checks; docs checks;
test discovery; duplication check. Platform-specific cases remain skipped on
macOS. No installed provider or device behavior was verified.

src/gpu/GpuCodeObjectsProvider.ts

@@ -102,7 +102,7 @@ export class GpuCodeObjectsProvider implements GpuCodeObjectsPort {
             input.path,
             this.#resources,
             options?.signal,
-            (file) =>
+            ({ handle: file }) =>
               this.#read(file, input, options?.signal, (value) => {
                 progress = value;
               }),