fix(workspaces): validate prospective child source trust

Pass server-owned creation context before the child is saved. Validate the
creator run, sponsor and parent ancestry against the immutable boundary,
then verify current parent and prospective child policies. Preserve exact
saved task identity for ordinary selection and writes.

Add real database and authenticated HTTP regressions, including omitted
client policy, and update the plan and paired workspace maps.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

maps/agent-access-map/workspaces.md

@@ -42,6 +42,7 @@ source projects' trust boundaries. Incompatible choices are rejected before
 dispatch; a projectless alias cannot bypass required sandbox containment.
 Source-copy checks apply the same trust boundary before provisioning. Low-trust
 sandbox runs skip host worktree provisioning, including built-in scripts.
+Child creation by an admitted agent checks an explicit prospective-task context before the child is saved. The creator run must have an authoritative saved policy and a verified company/agent/parent lineage. Current parent, prospective child and physical source policies must fit that boundary. This creation path does not relax exact task/run checks for existing-task writes. The [child trust regression](../../server/src/__tests__/task-workspace-child-trust.test.ts) is automated source-level evidence, not live agent qualification.
 Source review for these additions: PR #15749 and
 [task workspace routes](../../server/src/routes/task-workspaces.ts),
 [native authority](../../server/src/services/native-runtime/paperclip-runner-tool-authority.ts),