emrg: installer: write bin\pyvenv.cfg on Windows so bundled python venv works (#966 follow-up)

[pm25coder]

Follow-up to #966 (POSIX venv fix). On Windows, the bundled bin\python.exe / bin\python3.exe are copies of the python-dist interpreter and require a same-directory pyvenv.cfg to locate the stdlib — without it, python -m venv <dir> produces a venv whose python fails with Could not find platform independent libraries + ModuleNotFoundError: No module named 'encodings', blocking tasks that install research dependencies.

Driving rant (verbatim):

install 打包 Python 创建的 venv 不可用（pyvenv.cfg home 路径错误），任务无法安装科研依赖 — ~/.emrg/install/bin/python（Python 3.13.9）执行 python -m venv

生成的 pyvenv.cfg 中 home = ~/.emrg/install/bin，但解释器实际位于 ~/.emrg/install/bin/python-dist/bin/ —— home 路径错误导致 venv 内 python 无法定位标准库（Could not find platform independent libraries + ModuleNotFoundError: No module named 'encodings'）

Changes:

• packaging/make-installer.sh: new Inno [Code] procedure WritePyvenvCfg runs on ssPostInstall, writing {app}\bin\pyvenv.cfg with home = {app}\bin\python-dist (absolute path via ExpandConstant — a relative home fails with Failed to import encodings, verified locally). CfgContent is declared AnsiString to match SaveStringToFile's signature (same rule as the existing LogText precedent).
• packaging/smoke-test.sh: item 14 now exercises bin\python.exe on Windows — regenerates the same cfg in-test (mirroring the installer's ssPostInstall) with an absolute home, then runs python -m venv and verifies stdlib import + pip. POSIX path unchanged (bin/python wrapper from emrg: packaging: fix bundled python venv (pyvenv.cfg home) via bin/python wrapper #966).
• emrg/server/prompts/upgrade_prompt.j2: instructs the upgrade agent to write bin/pyvenv.cfg with the native absolute path during local equivalent installs.
• tests/test_installer_stop.py: pure-text regression test pinning the new wiring (procedure presence, AnsiString declaration, absolute-home content, CurStepChanged ordering, smoke Windows branch, upgrade-prompt mention).
• Agent.md: doc-count guard sync (1051 → 1052).

Verified locally: pytest 987 passed / 65 skipped, import + CLI checks green, Windows venv regression (bin\python.exe -m venv → venv OK, pip 25.2). Full installer/Inno compilation is validated by the windows Build Release CI.

[argszero]

✅ LGTM — cycle

Reviewed the full diff against rant 2026-08-24T21:46:53 (#966 Windows follow-up):

• make-installer.sh: WritePyvenvCfg writes {app}\\bin\\pyvenv.cfg with absolute home = {app}\\bin\\python-dist (ExpandConstant), called in ssPostInstall BEFORE AddBinDirToPath. CfgContent: AnsiString matches Inno Setup 6.7.1+ SaveStringToFile signature (UnicodeString would fail to compile) — the dedicated test pins this exactly. CRLF (#13#10) correct for Windows.
• smoke-test.sh: Windows branch (${WINDIR:-}) replicates the installer-written cfg with cygpath -w absolute path and exercises bin\python.exe directly — good that the 'missing DLL' R100 conclusion is corrected (DLLs are in bin; the real missing piece was the cfg).
• upgrade_prompt.j2: local-equivalent install also writes bin/pyvenv.cfg with native absolute path, POSIX skip documented — symmetric with the installer path.
• Test: text-assertion regression test (no iscc/cmd execution, CI-safe) covering installer [Code], smoke-test branch, and upgrade prompt; Agent.md count 1051→1052 consistent (doc-count guard green).
• CI: test + test-windows both green (run 32799604676).

Solid follow-up completing the #966 story on Windows.

[argszero]

✅ LGTM — cycle (2/3)

Re-checked this cycle: head 4c709a6 unchanged, CI test + test-windows still green (run 32799604676). Confirmations from re-review:

• WritePyvenvCfg uses AnsiString for SaveStringToFile (Inno Setup 6.7.1+ signature — UnicodeString would not compile) and writes CRLF-terminated home = {app}\bin\python-dist absolute path.
• ssPostInstall ordering: WritePyvenvCfg before AddBinDirToPath (pinned by the regression test).
• smoke-test.sh Windows branch replicates the cfg via cygpath -w absolute path before exercising bin\python.exe — consistent with the installer path.
• upgrade_prompt.j2 covers local-equivalent installs (POSIX skip documented) — symmetric.
• Doc count 1051→1052 matches the new test (#511 guard green).

No issues found; ready to merge once the 3rd LGTM lands.

[argszero]

✅ LGTM — cycle (3/3)

Final re-check: head 4c709a6 unchanged, CI test + test-windows green (run 32799604676), MERGEABLE. Three consecutive LGTMs from distinct cycles (100311, 101045, 101729) with no ❌. Windows pyvenv.cfg story (#966 follow-up) complete — merging.