Use external temporary storage for release builds

docs/internal/overview.md

@@ -39,6 +39,7 @@ these implemented packages:
 | `internal/delivery` | Tagged-checkout verification, artifact inventory/hash validation, manifest assembly, and coordination of hosted delivery results. |
 | `internal/git` | Git command boundary, push-destination resolution, exact ref inspection, and tag operations. |
 | `internal/gitea` | Gitea API transport, hosted release pages, asset inspection, manifests, and uploads. |
+| `internal/tempdir` | Disposable system temporary storage outside source worktrees. |
 | `internal/process` | Cancellable child-process execution with per-command environment overlays. |
 | `internal/publish` | Publication guards, one validation run, annotated tag creation, push, and recovery state. |
 | `internal/runtimeinfo` | Private version lookup used by the runtime facade. |

docs/roadmap/remediation.md

@@ -230,6 +230,8 @@ offline suite, and compiled-export/import checks pass.
 
 ### R6 — Medium: Builds require a writable parent of the repository
 
+Status: Resolved.
+
 Category: Inadvertently strengthened filesystem prerequisite.
 
 **Evidence:** [Candidate builds](../../internal/build/candidate.go), around line 21,
@@ -250,6 +252,11 @@ adding broad output-directory restrictions.
 read-only repository parent and a usable system temporary directory. Generated
 candidate output still leaves the worktree clean.
 
+**Resolution:** Candidate and CLI delivery builds use shared system temporary
+storage allocated by `internal/tempdir`, with worktree containment checks and
+caller-owned cleanup. Regressions execute both operations with read-only
+repository parents and confirm clean worktrees. Affected suites pass.
+
 ### R7 — Medium: Attachment origin restrictions exceed credential isolation
 
 Category: Inadvertently strengthened prohibition.