PYSEC-2026-4013

virtualenv bash and fish activation scripts execute commands embedded in paths

The generated `activate` (bash/zsh) and `activate.fish` scripts interpolate a `shlex.quote`-ed value into a position that quotes it a second time. The extra quotes terminate the quoted run early and leave part of the value parsed as shell code, so a path containing shell metacharacters runs commands when a user sources the activation script. `activate` is affected through the virtual environment's own path, on the branch that reports a relocated environment (`Virtual environment directory __VIRTUAL_ENV__ does not exist!`). For a destination named `x'$(id)'y`, `shlex.quote` emits `'x'"'"'$(id)'"'"'y'`; the inner `"` closes the enclosing double quote and `$(id)` is left unquoted. This branch runs whenever the recorded path is absent, which is the normal case for a virtual environment copied or distributed to another machine. `activate.fish` is affected through the interpreter's Tcl/Tk library paths (`set -gx TCL_LIBRARY '__TCL_LIBRARY__'`). The rendered line becomes `''/tcl/(cmd)/lib''`, and fish expands the `(cmd)` left between the adjacent quoted runs. The same doubling splits a path containing a space into two list elements, corrupting `TCL_LIBRARY` and `TK_LIBRARY`. This is the same defect class as GHSA-x78j-v8h9-3j2q, which covered `activate.bat`. Fixed in 21.7.13 by moving the placeholders outside the surrounding quotes, so each value keeps only the quoting `shlex.quote` applied.