fix(harness): normalize materialized checkouts and stop the harness layer stranding the device

[rldyourmnd]

Found by running the 2.3.0 apply on a real Ubuntu 26.04 desktop. It failed with:

nddev-codex: error: nddev-builder source plugin tree must not be writable by group or others

Cause, and why it belongs here

git clone and git checkout create files under the caller's umask. Under umask 002 the materialized harness checkout landed with 252 group-writable paths, and nddev-codex-app's install-builder then correctly refused it - after rldyour::_ensure_pinned_git_checkout had already reported success. The refusal is right; producing the tree that trips it is this repository's bug.

rldyour::_harness_checkout_permissions now normalizes through the shared managed-tree helper (no third permission implementation) on both paths:

• the clone path, and
• the fast path, which is the only one a host with an already-pinned clean checkout ever takes again. Skipping it there would leave such a host permanently unable to bootstrap - which is exactly the state the reporting device was in.

Normalizing rather than refusing is safe: the bytes are provably the pinned commit, so tightening their modes cannot change what gets installed. Refusing would instead brick every umask 002 host.

Measured on the real broken tree: 252 -> 0 group-writable paths, and the module's guard then accepts it.

The defect that fix exposed

With the permission cause removed, the failure moved to a second, independent guard in the same module (a stale local builder profile). That makes the real problem plain: the harness layer sat ahead of every other layer while depending on local state this repository does not own.

This is the same pathology ADR 0006 removed for zcode, with the same consequence - the reporting desktop was missing 24 of the 46 commands verify.sh requires, because one delegated guard aborted the run before the language servers, compiled hosts, pinned scanners, browser stack, and rtk.

Both installers now run the harness layer last, immediately before verification. The step stays fatal - it is not softened into warn-and-continue, which this repository forbids - but it is now fatal to itself instead of to the whole device.

Evidence

Check	Result
python3 -m pytest	96 passed (+2 new invariants)
scripts/ci/lint.sh	scripts-lint-ok
bash -n on all three edited scripts	clean
permission fix on the real tree	252 -> 0; module guard now passes

Two tests pin the invariants so neither can silently regress: the harness layer must run after install_browser_providers and install_rtk in both installers while staying fatal, and both checkout paths must call the shared normalizer.