Provision nodejs/python3/unzip for mason.nvim installers

mason.nvim (externally-managed Neovim dotfiles config) was failing to
install several LSP servers and tools because npm, python3, and unzip
weren't on PATH in the Home Manager profile.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BBSd4VBfoKHjE1HR3P8kmn

4 files changed, 104 insertions, 0 deletions

diff --git a/openspec/changes/fix-mason-installer-deps/.openspec.yaml b/openspec/changes/fix-mason-installer-deps/.openspec.yaml
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+schema: spec-driven
+created: 2026-09-21
diff --git a/openspec/changes/fix-mason-installer-deps/proposal.md b/openspec/changes/fix-mason-installer-deps/proposal.md
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+## Why
+
+`mason.nvim` (managed by the externally-owned, Stow-linked Neovim dotfiles config)
+fails to install several LSP/tooling packages on this flake's Home Manager profile:
+`pyright`, `bash-language-server`, `yaml-language-server`,
+`typescript-language-server`, `css-lsp`, and `html-lsp` fail because `npm` is not on
+`PATH`; `debugpy` fails because no `python3`/`python` is on `PATH`; `terraform-ls`
+fails because `unzip` is not on `PATH`. `programs.neovim.withPython3 = true` only
+wires up Neovim's Python *provider* (pynvim) and does not put a `python3` binary on
+`PATH`, so it does not cover this. `js-debug-adapter` and `lua-language-server`
+already install successfully and need no change.
+
+## What Changes
+
+- Provision `nodejs` (for `npm`), `python3`, and `unzip` on `PATH` via the shared
+  Home Manager profile, so `mason.nvim`'s installers can find the interpreters/tools
+  they shell out to.
+
+## Capabilities
+
+### New Capabilities
+- `editor-toolchain`: The shared home-manager profile provisions the runtime
+  toolchain (interpreters, package managers, archive tools) that the externally
+  Stow-managed Neovim/mason.nvim config depends on to install and run LSP servers
+  and debug adapters, without home-manager owning any of that config itself.
+
+### Modified Capabilities
+(none — `developer-environment` covers general most-used CLI tools, not the
+Neovim/mason.nvim dependency contract, so a new capability is used instead of
+overloading that one.)
+
+## Impact
+
+- `modules/home/editor.nix`: extend the existing `home.packages` list (already used
+  for `tree-sitter`/`stdenv.cc`, the same "tools the dotfiles-owned nvim config
+  needs" pattern) with `nodejs`, `python3`, `unzip`.
+- Applies to both Home Manager configs that import this module — `tom@linux` and
+  `tom@darwin` (per `flake.nix`) — covering all supported systems.
+- No changes to the externally-managed dotfiles/Neovim Lua config itself.
diff --git a/openspec/changes/fix-mason-installer-deps/specs/editor-toolchain/spec.md b/openspec/changes/fix-mason-installer-deps/specs/editor-toolchain/spec.md
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+++ b/openspec/changes/fix-mason-installer-deps/specs/editor-toolchain/spec.md
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+## Purpose
+
+Provisions, via the shared home-manager profile, the runtime toolchain that the
+externally Stow-managed Neovim/mason.nvim config depends on to install and run LSP
+servers, formatters, and debug adapters — without home-manager owning that editor
+config itself.
+
+## ADDED Requirements
+
+### Requirement: mason.nvim installer dependencies are provisioned
+The shared home-manager profile SHALL include a Node.js runtime (providing `npm`), a
+Python 3 interpreter (providing `python3`), and `unzip` on `PATH`, so that
+`mason.nvim`'s package installers can locate the tools they shell out to.
+
+#### Scenario: npm-based Mason package installs successfully
+- **WHEN** the shared home profile is activated and `mason.nvim` installs an
+  npm-based package (for example an LSP server distributed via npm)
+- **THEN** `mason.nvim`'s installer finds `npm` on `PATH` and the installation does
+  not fail with an `ENOENT`/"could not find executable" error for `npm`
+
+#### Scenario: Python-based Mason package installs successfully
+- **WHEN** the shared home profile is activated and `mason.nvim` installs a
+  Python-based package (for example `debugpy`)
+- **THEN** `mason.nvim`'s installer finds a `python3` interpreter on `PATH` and the
+  installation does not fail with a "no python3 installation found" error
+
+#### Scenario: Archive-based Mason package installs successfully
+- **WHEN** the shared home profile is activated and `mason.nvim` installs a package
+  distributed as a zip archive (for example `terraform-ls`)
+- **THEN** `mason.nvim`'s installer finds `unzip` on `PATH` and the installation does
+  not fail with an `ENOENT`/"could not find executable" error for `unzip`
+
+### Requirement: Editor toolchain packages do not manage editor configuration
+Packages provisioned by this capability SHALL supply only the underlying
+interpreters/tools that the externally-managed Neovim dotfiles config depends on;
+this capability SHALL NOT generate, own, or otherwise manage any Neovim
+configuration file (for example `init.lua` or plugin/LSP configuration).
+
+#### Scenario: No competing Neovim configuration is generated
+- **WHEN** the shared home profile provisions the editor toolchain packages
+- **THEN** no Neovim configuration file is created or managed by this capability —
+  the externally Stow-managed dotfiles config remains the sole owner of that
+  configuration
diff --git a/openspec/changes/fix-mason-installer-deps/tasks.md b/openspec/changes/fix-mason-installer-deps/tasks.md
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+++ b/openspec/changes/fix-mason-installer-deps/tasks.md
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+## 1. Provision editor toolchain packages
+
+- [x] 1.1 In `modules/home/editor.nix`, add `nodejs`, `python3`, and `unzip` to the
+      existing `home.packages` list (alongside `tree-sitter`/`stdenv.cc`), with a
+      short comment noting they're required by `mason.nvim`'s installers; verify by
+      reading the file back and confirming the three entries are present.
+- [ ] 1.2 Verify the flake still evaluates: run `nix flake check` and confirm it
+      succeeds.
+
+## 2. Verify Mason installs succeed
+
+- [ ] 2.1 Apply the profile on an affected host (`home-manager switch --flake
+      .#tom@linux` or `.#tom@darwin`, whichever is reachable) and confirm the
+      activation completes without error.
+- [ ] 2.2 In Neovim, delete `~/.local/state/nvim/mason.log` (or run `:MasonUninstallAll`
+      then reinstall), trigger installation of the previously-failing packages
+      (`pyright`, `bash-language-server`, `debugpy`, `terraform-ls`,
+      `yaml-language-server`, `typescript-language-server`, `css-lsp`, `html-lsp`),
+      and confirm `:Mason` reports them all installed with no `npm`/`python3`/`unzip`
+      "could not find executable" errors in the new log.