feat!: simplify R executable / console path settings - #1735

Close #597
Close #1437
Supersede #1625

Related to #1130

Summary

• add r.executablePath as the canonical vanilla R executable for language-server and other background processes
• add r.consolePath as the canonical interactive console executable, including bare executable names resolved from PATH (for example, arf or radian)
• formally deprecate the six platform-specific r.rpath.<platform> and r.rterm.<platform> settings while preserving them as compatibility inputs
• remove the unreleased r.rterm.preferredConsoles setting and the previously deprecated, unused r.helpPanel.rpath setting
• add host-independent regression coverage for precedence, PATH and registry discovery, substitutions, quoting, and workspace edge cases
• resolve executable settings and ${workspaceFolder} against the relevant workspace or document resource when one is available

Why these names?

The names follow the convention used by other VS Code language extensions: for example, Python uses python.defaultInterpreterPath, Julia uses julia.executablePath, and Ruby LSP uses rubyLsp.rubyExecutablePath. executablePath clearly identifies the vanilla executable used by the extension, while the parallel consolePath name preserves vscode-R's important distinction between background R and an alternative interactive console.

We cannot use the shorter r.rpath and r.rterm while retaining their legacy platform-specific children: VS Code treats dotted configuration identifiers hierarchically, so scalar parent settings conflict with r.rpath.windows, r.rterm.linux, and the other existing keys. The Path suffix also makes clear that these settings select an executable location (including a name resolved from PATH), rather than configuring console behavior more broadly.

Resolution rules

Background/vanilla R resolves in this order:

1. r.executablePath
2. legacy r.rpath.<current platform>
3. R on PATH
4. Windows registry InstallPath (Windows only)

The interactive console resolves in this order:

1. r.consolePath
2. legacy r.rterm.<current platform>
3. an explicitly configured r.executablePath
4. system R (PATH, then the Windows registry)

The distinction between background R and the interactive console remains intentional: background processes never use r.consolePath or legacy r.rterm.<platform>. Also, a legacy r.rpath.<platform> override does not begin controlling the console; only the new canonical r.executablePath can provide that default.

Both canonical settings use machine-overridable scope because executable locations are machine-dependent while workspace overrides remain useful. Relevant terminal, language-server, task, R Markdown, C++ properties, and command call sites now pass their workspace or document URI so folder-level settings and ${workspaceFolder} substitution use the same resource. Empty values are treated as unset. Explicit but unavailable values fail instead of silently selecting a different executable.

Historical compatibility

The old settings were split by OS when defaults were hard-coded installation paths. The resolver keeps the later discovery behavior added for real-world installations:

• R on PATH takes priority over the Windows registry (Get R term path from registry in Windows #244, Use Windows registry to find R path #252, Prefer rPath from PATH #649)
• background commands use vanilla R, independently of alternative consoles (Clarify error messages #607, Integrate vscode-r-lsp #695 and commit 5e9c895)
• ${userHome}, ${workspaceFolder}, ${fileWorkspaceFolder}, and ${fileDirname} substitutions remain supported (allow to invoke R terminal also in relative paths #1398, Substitute variables in r.rpath and r.rterm settings #1444)
• quoted paths and paths containing spaces remain supported (Remove quotes from rpath if necessary #884)
• a bare name is looked up on PATH, never interpreted as a workspace-relative path (Search for r.rterm.linux/mac on system PATH #1347, Executable name is resolved as relative terminal path #1437)

The platform-specific settings remain supported for backward compatibility but are deprecated in favor of the canonical settings and may be removed in a future release.

Scope boundaries and deliberate follow-ups

• .github/ISSUE_TEMPLATE/bug_report.md intentionally remains unchanged even though it contains legacy setting examples. The template needs a broader rewrite, which will be handled separately rather than partially updating it in this PR.
• This PR makes executable configuration lookup resource-aware, but does not introduce a complete per-folder runtime lifecycle. In particular, it does not restart the help subsystem when the active folder changes or redesign single-/multi-server LSP lifecycle behavior.