test(architecture): pin UTF-8 fixture I/O and tolerate unprivileged symlinks

[JasonBuildAI]

Goal And Delivered Outcome

Native Windows contributors whose ANSI code page is not UTF-8 (e.g. zh-CN/cp936) and who cannot create symlinks get 12 red tests/architecture checks that fail before reaching any assertion, so the vocabulary-drift and RFC-governance guards cannot be trusted as a local pre-push signal on a supported platform; after this PR the same suite is green on such a host with no behavior change on UTF-8 hosts or CI.

• Outcome basis / optional anchor: [Bug]: tests/architecture reports 12 host-dependent failures on native Windows (cp936 locale, no symlink privilege) #6233 (reproduced defect; no roadmap id).
• Goal/source and gap: on upstream 43643a5e5, pytest tests/architecture on a cp936, symlink-unprivileged Windows checkout reports 12 failed, 1421 passed; 11 failures are host-codec UnicodeDecodeErrors in fixture text I/O and 1 is WinError 1314 from a direct symlink_to in a fixture.
• Observable before → after, with the validation row that proves it: 12 failed, 1421 passed → 1432 passed, 1 skipped (Validation unit and regression_parity rows).
• Issue/task and intended base: Closes [Bug]: tests/architecture reports 12 host-dependent failures on native Windows (cp936 locale, no symlink privilege) #6233; base main (upstream 43643a5e5).

Author Declaration

• Written by: model_agent (OpenAI Codex CLI agent) operating the JasonBuildAI contribution account.
• AI disclosure: this change was drafted with AI assistance at my request, under my direction and review.

Implemented against

• Specification and revision: no written specification; the linked issue [Bug]: tests/architecture reports 12 host-dependent failures on native Windows (cp936 locale, no symlink privilege) #6233 (reproduced on upstream 43643a5e5) is the basis.
• Criteria:

Criterion (spec clause)	Disposition	Symbol / path	Test or command
Issue #6233: tests/architecture passes on native Windows with cp936 locale and no symlink privilege	implemented	tests/architecture/test_semantic_production.py, tests/architecture/test_contributor_task_board.py, tests/architecture/test_rfc_status_index.py, tests/architecture/test_semantic_inventory.py	uv run --extra test python -m pytest tests/architecture -q -> 1432 passed, 1 skipped
Fixture text I/O no longer lets the host locale decide how repo content is decoded, or writes fixture content the UTF-8 owner cannot read	implemented	same four files (encoding kwargs only)	before/after comparison in Validation rows
The symlink rejection arm still runs wherever symlink creation is possible	implemented	test_semantic_inventory.py::test_tracked_symlink_cannot_read_untracked_source	skip only on OSError from symlink_to; unchanged body runs on ubuntu CI

• Self-check before submission: ran the full architecture suite on the same commit with the diff reverted and re-applied (git apply -R, reverted after capture), ran the four files under PYTHONUTF8=1 to simulate a UTF-8 host, and ran ruff check on the changed files. Did not touch product code, dependencies, or unrelated tests.

Scope And Continuation

• Completed scope and remaining work: complete within this scope. The audit is bounded to tests/architecture; other suites were not swept for the same host-codec pattern and no failure was observed outside this directory.
• Slice boundary / successor: N/A - the suite is the whole surface this change serves.

Validation

• Tested revision: cbc00b6
• Run state: finished
• Input classes: synthetic, public_fixture

Check kind	Result	Public-safe evidence / limitation
unit	passed	uv run --extra test python -m pytest tests/architecture -q on Windows/cp936, Python 3.12: before 12 failed, 1421 passed; after 1432 passed, 1 skipped.
regression_parity	passed	Same-commit baseline (diff reverted with git apply -R) vs fixed head; PYTHONUTF8=1 run of the four affected files: 90 passed, 1 skipped, i.e. UTF-8 hosts see no behavior change.
static	passed	uv run --extra test python -m ruff check over the four changed files -> All checks passed!
integration	not_run	The symlink arm cannot execute on hosts without symlink privilege; the unchanged test body runs in the existing ubuntu python-tests workflow.

• Coverage and gaps: the 12 previously failing checks cover every changed call site; the symlink assertion is skipped only where the OS refuses symlink creation (CI covers it). No product code, CLI, or API surface is affected.

Frontend / Visual Evidence

• UI impact: none

Type of Change

• Test update

LoopX Area

• Build, packaging, installer, or CI

Technical Direction

• Direction / acceptance reference, when applicable: N/A

Shared-authority RFC fixture impact

N/A

Boundary Checklist

• Neither the diff nor this PR body/comments/attachments disclose private state, credentials, raw traces or verifier output, internal links, or local machine paths (including .loopx/, .codex/goals/, and live ACTIVE_GOAL_STATE.md).
• I did not duplicate maintainer-owned benchmark work unless a maintainer split out a public issue for it.
• I kept the change scoped to the linked issue/task.
• I completed the visual evidence section for UI changes, or marked UI impact none.
• Every commit includes a DCO Signed-off-by trailer (git commit -s).