AGENTS.md: User Preferences trap - unconverted Windows paths under POSIX shells

A C:/... path handed unconverted to a POSIX file command under WSL or
msys/git-bash is a relative path: it silently creates a stray cwd tree
whose first component is literally named 'C:' (the NTFS-illegal colon
stored as private-use character U+F03A), invisible to git and fossil
while it contains only empty directories. Remedy: translate at the
boundary (wslpath/cygpath - msys auto-conversion does not cover quoted
command strings or MSYS_NO_PATHCONV/MSYS2_ARG_CONV_EXCL sessions) and
glance at the repo root for stray C* entries after WSL/msys-driven work.
Origin: G-140 WSL smokes leaked an empty temp-dir skeleton into the repo
root, found and removed 2026-07-31.

Assisted-by: harness=claude; primary-model=claude-fable-5; api-location=anthropic.com

AGENTS.md

@@ -95,6 +95,7 @@ When the user requests a durable behavior change, record it here or in the relev
 - LF line endings are strongly preferred for all files in this repository. Converting a CRLF text file to LF when an edit touches it is correct and welcome - do not preserve CRLF for diff-minimisation. Preserve existing line endings only for files with deliberately mixed/CRLF endings (e.g. line-ending round-trip test data) or when explicitly instructed for a file.
 - If the active editor is on a source-derived snapshot, bootstrap copy, or build output path such as `src/bootsupport/`, root `modules/`, root `lib/`, `modules_tcl8/`, `modules_tcl9/`, `lib_tcl8/`, or `lib_tcl9/`, confirm the intended target before editing unless the user explicitly named that path.
 - cmd.exe PATH truncation (this machine, and any Windows machine with a heavily populated PATH): cmd.exe truncates a long PATH, so a tool that resolves fine in PowerShell may be "not found" when invoked via `cmd.exe /c`. Use absolute executable paths inside any `cmd /c` command line, and prefer PowerShell-native invocation unless a console host is specifically required (e.g. hidden-console test harnesses). If a tool is missing only under cmd.exe, suspect truncation before absence.
+- Windows paths under POSIX shells (WSL, msys/git-bash): a `C:/...` path passed unconverted to a POSIX file command (`mkdir -p`, `cp`, output redirects) is a RELATIVE path - it silently creates a stray directory tree in the cwd whose first component is literally named `C:` (the NTFS-illegal `:` is stored as private-use character U+F03A, so it renders as `C` plus an odd dot/glyph in Explorer, and while the tree contains only empty directories it is invisible to git and fossil). Translate at the boundary (`wslpath` for WSL, `cygpath` for msys - msys auto-conversion does NOT cover paths inside quoted command strings or when MSYS_NO_PATHCONV/MSYS2_ARG_CONV_EXCL is set), and after WSL/msys-driven work glance at the repo root for a stray `C*` entry. (Origin: G-140 WSL smokes leaked an empty temp-dir skeleton into the repo root, found and removed 2026-07-31.)
 - Agent-authored text is plain ASCII by default: no em/en dashes, curly quotes, arrow or ellipsis characters, or other typographic Unicode - use ASCII equivalents (" - ", straight quotes, "->", "..."). The rule governs elements the agent generates, with extra force for outward-bound artifacts (ticket drafts, bug reports, emails, commit messages - anything likely to be pasted into an external system), which are verified before handover (e.g. grep for `[^\x00-\x7F]`). The exceptions are illustrative, not a closed list: non-ASCII subject matter (encoding/Unicode/ANSI-art test data, or documentation demonstrating such behaviour), verbatim quotes of existing material, and explicit user request are the common cases, but any good reason qualifies - state the reason when deviating. Content the agent did not author is outside the rule: existing files are never bulk-retrofitted, and while checking non-authored content (e.g. files being committed on the user's behalf) is fine, non-ASCII there is the author's prerogative - if unsure whether it is intentional, stop and ask rather than fix or block.
 - Tcl has no `-e`/`-c` one-liner flag (a reflex agents carry over from perl/python/node). Stock `tclsh`/`tclsh86`/`tclsh90` recognise only `-encoding name` as a leading option; any other argument starting with `-` is NOT treated as a script file - all arguments land in `$argv` and tclsh reads commands from stdin. On a console that hangs forever at an interactive prompt; with piped/redirected stdin it exits 0 having silently ignored the supposed one-liner and executed stdin instead. (The punk kits differ: they treat `-e` as a script filename and error out immediately - no hang, but still no one-liner.) To run ad-hoc Tcl: write a temp `.tcl` file and run `tclsh path/to/file.tcl`, or pipe the script to stdin (`echo 'puts hi' | tclsh`, or a bash heredoc). Defensive habit regardless: when exec'ing tclsh non-interactively, redirect stdin (`</dev/null`, `< NUL`) so a mis-invocation exits at EOF instead of hanging.
 - For ad-hoc punkshell scripts that need working-tree modules, use `bin/punk91 src script` for stdin scripts or `bin/punk91 src script path/to/file.tcl` for script files. Do not use `bin/punk91 src` for piped/redirected snippets: `src` alone starts the live shell on the repo source tree and may execute stdin input but then remain in shell/eof handling instead of exiting cleanly. Keep `src` before `script` so the working-tree modules are loaded.