feat: preflight - prerequisites checked and tool paths recorded before wikitool runs; launcher refuses without it (#151, POSIX half)

Files changed:
- .claude/settings.json
- .gitea/workflows/ci.yml
- .gitea/workflows/nightly.yml
- .gitea/workflows/release.yml
- .gitea/workflows/tracker-live.yml
- .github/hooks/wiki-trace.json
- .gitignore
- .vibe/hooks.toml
- AGENTS.md
- CHANGES.md
- EVALS.md
- INSTALL.md
- README.md
- VERSION
- instructions/bootstrap.md
- instructions/preflight.md
- instructions/setup-instance.md
- instructions/upgrade-instance.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/cli.py
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/commands/git_publish.py
- tools/chemenu/commands/migrate_cmd.py
- tools/chemenu/config.py
- tools/chemenu/corpus_cache.py
- tools/chemenu/prerequisites.py
- tools/chemenu/search/ripgrep.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_dist_upgrade.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_preflight.py
- tools/chemenu/toolpaths.py
- tools/preflight.sh
- tools/prerequisites.txt
- tools/run_wikitool.py
- tools/trace-hook
- tools/wikitool

tools/prerequisites.txt

@@ -0,0 +1,22 @@
+# What this stack needs on the machine, read by tools/preflight.sh, tools/preflight.ps1
+# and `wikitool doctor` - one list, so the three cannot disagree. The procedure around it
+# is instructions/preflight.md.
+#
+# Line format, fields separated by `|` so a POSIX shell reads it with `IFS='|' read`:
+#
+#   limit|<name>|<value>
+#   tool|<name>|<minimum version, or ->|<all or windows>|<label>|<why it is needed>|<choco>|<winget>|<brew>|<apt>|<pacman>
+#
+# A `-` in an install field means that package manager has no entry for this tool.
+# `name` is the key the tool is recorded under in .wikitool-tools.json.
+
+# The longest install folder - the directory holding tools/ - that still fits Windows'
+# MAX_PATH of 259 when long paths are off: 95 + 1 separator + the 160 characters
+# `titles.PATH_BUDGET` gives a file below the instance root, with 3 to spare.
+# Change it only together with that budget; a test holds the two to the sum.
+limit|install_dir_max|95
+
+tool|python|3.11|all|Python|every wikitool command runs on it|choco install python|winget install --id Python.Python.3.13 -e|brew install python|sudo apt install python3 python3-venv|sudo pacman -S python
+tool|git|-|all|Git|the wiki is a git repository, and publishing commits through git|choco install git|winget install --id Git.Git -e|brew install git|sudo apt install git|sudo pacman -S git
+tool|rg|-|all|ripgrep (rg)|search and several checks read the wiki through it|choco install ripgrep|winget install --id BurntSushi.ripgrep.MSVC -e|brew install ripgrep|sudo apt install ripgrep|sudo pacman -S ripgrep
+tool|pwsh|7|windows|PowerShell 7 (pwsh)|the agent harnesses on Windows run their commands in it|choco install powershell-core|winget install --id Microsoft.PowerShell -e|-|-|-