[Reopen request] .jsonc missing from LANGUAGE_EXTENSIONS makes JSON/JSONC configs undiagnosable (closed NOT_PLANNED in #15859)

Requesting reconsideration of #15859 (closed NOT_PLANNED, 2026-07-03). The .jsonc gap it names is still present on 1.18.30 and now has a concrete, user-visible impact plus a one-line fix.

Mechanism

.jsonc is absent from LANGUAGE_EXTENSIONS, so the LSP didOpen languageId falls back to "plaintext". Servers that dispatch on languageId (biome, and the standard JSON LS) then ignore the document entirely.

packages/opencode/src/lsp/language.ts:1    export const LANGUAGE_EXTENSIONS: Record<string, string> = {
packages/opencode/src/lsp/language.ts:53     ".json": "json",        // no ".jsonc" key anywhere in the map
packages/opencode/src/lsp/client.ts:560    const languageId = LANGUAGE_EXTENSIONS[extension] ?? "plaintext"

packages/opencode/src/lsp/server.ts:296ΓÇô325 lists .jsonc in Biome's extensions, so the file is routed to the server ΓÇö it just arrives as plaintext.

Impact (why this is worth the one line now)

Both opencode-family config files are .jsonc: ~/.config/opencode/opencode.jsonc and OMO's ~/.omo/omo.jsonc. With this gap, neither can get diagnostics from any JSON language server ΓÇö including the schema validation that would catch unsupported keys. That directly blocks the workflow in #41014 (schema validation for opencode.jsonc), where I verified the published schema yields no diagnostics.

Side-by-side repro (identical bytes, bare dir, "lsp": true)

broken.json   -> <diagnostics ...> ERROR [4:1] Expected an array, an object, or a literal but instead found '}'.
broken.jsonc  -> (no <diagnostics> block for this file)

Second probe with a schema violation and $schema in the document:

probe2.json   -> (no diagnostic ΓÇö separate issue, #41014)
probe2.jsonc  -> (no diagnostic)

Independent confirmation that the server can handle .jsonc: through oh-my-openagent's own lsp_diagnostics path the same file reports error[biome] (parse) at 4:0: Expected an array, an object, or a literal but instead found '}'.

Expected vs actual

Expected: .json and .jsonc behave identically (both are JSON-with-comments; Biome supports both).
Actual: .json gets diagnostics; .jsonc is silently skipped.

Proposed fix

".jsonc": "jsonc",

(plus the other omissions already listed in #15859: .toml, .mdx, .pyi, .h/.hpp/.hh/.hxx/.h++, .R, and the bare makefile key). Related: #23663 (closed NOT_PLANNED) reported the same plaintext fallback for custom servers.

Verified 2026-09-13, opencode 1.18.30 (Windows 10 Pro 19045), plugin oh-my-openagent 4.19.4.

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Environment (software)

item	value
OS	Microsoft Windows 10 Pro — 10.0.19045 (Build 19045), 64-bit
Shell	PowerShell 7.6.6 (+ Windows Terminal)
opencode	1.18.30
plugins	oh-my-openagent 4.19.4 · @cortexkit/opencode-antigravity-auth 2.2.1
runtimes	Node v24.19.0 · npm 11.17.0 · Bun 1.4.2
LSP binaries	biome 2.5.13 · basedpyright 1.40.1 · roslyn-language-server 5.12.0-1.26426.8 · bash-language-server 5.6.0 · shellcheck 0.11.0 · vscode-langservers-extracted 4.10.0 · PowerShellEditorServices 4.7.0 · PSScriptAnalyzer 1.25.0
logs	~/.local/share/opencode/log/opencode.log · ~/.omo/agent/OmO-debug.log · ~/.omo/agent/logs/config-reload.log

OS facts collected with:

Get-CimInstance Win32_OperatingSystem | Select-Object Caption,Version,BuildNumber,OSArchitecture

No hardware, hostname, username, or credentials included.