fix(cli): fall back to settings.json when Claude Code binary is unresolvable (#6701) (#6734)

getCliRuntimeStatus() only ever answered `installed` from binary resolution
(known install paths + where/which PATH search), so a stale PATH, moved
binary, or uncatalogued install method reported "not found" even when
~/.claude/settings.json proved the CLI was installed and used before —
regressing behind upstream 9router's checkClaudeInstalled(), which already
falls back to the settings file when where/which fails.

withSettingsFallback() (new src/shared/services/cliInstallFallback.ts, kept
out of the frozen cliRuntime.ts to respect its file-size ceiling) restores
that parity: only when the binary lookup's own reason is "not_found" (never
for deliberate security rejections like unsafe/relative env overrides or
symlink escapes) and the tool's settings file exists on disk.

src/shared/services/cliInstallFallback.ts

@@ -0,0 +1,69 @@
+import fsSync from "fs";
+
+/**
+ * #6701 — 9router-parity fallback for CLI install detection.
+ *
+ * `getCliRuntimeStatus()` in `cliRuntime.ts` determines `installed` from
+ * binary resolution alone (known install paths + a `where`/`which` PATH
+ * search). If the binary is not currently resolvable — stale PATH inherited
+ * by a long-running/background OmniRoute process, the binary having moved,
+ * or an install method we don't enumerate yet — it used to unconditionally
+ * report `installed:false`, even when the tool's own settings/config file on
+ * disk proves it was installed and used before.
+ *
+ * Upstream 9router's equivalent route
+ * (`src/app/api/cli-tools/claude-settings/route.js::checkClaudeInstalled()`)
+ * has a second-chance fallback: when `where`/`which` fails, it still reports
+ * `installed:true` if the settings file exists. This restores that fallback
+ * for any CLI tool that declares a `settings` config path (currently
+ * `claude` and `droid` — see `CLI_TOOLS` in `cliRuntime.ts`).
+ *
+ * Only applies when the lookup's own reason is "not_found" — i.e. the binary
+ * genuinely couldn't be located on PATH/known install paths. Deliberate
+ * security rejections (unsafe/relative env override paths, symlink escapes,
+ * suspicious file sizes, etc.) must stay `installed:false` regardless of
+ * whether a settings file happens to exist.
+ */
+export interface NotInstalledResult {
+  installed: false;
+  runnable: boolean;
+  command: string | null;
+  commandPath: string | null;
+  reason: string;
+  runtimeMode: string;
+  requiresBinary: boolean;
+}
+
+export interface SettingsFallbackResult {
+  installed: true;
+  runnable: false;
+  command: string | null;
+  commandPath: null;
+  reason: "settings_found_binary_unresolved";
+  runtimeMode: string;
+  requiresBinary: boolean;
+}
+
+/**
+ * Given the resolved settings-file path for a tool (or undefined if the tool
+ * has none) and the "not installed" result the binary lookup already
+ * produced, return a settings-fallback result when the settings file exists
+ * on disk, or the original "not installed" result unchanged otherwise.
+ */
+export const withSettingsFallback = (
+  settingsPath: string | undefined,
+  notInstalledResult: NotInstalledResult
+): NotInstalledResult | SettingsFallbackResult => {
+  if (notInstalledResult.reason !== "not_found") return notInstalledResult;
+  if (!settingsPath || !fsSync.existsSync(settingsPath)) return notInstalledResult;
+
+  return {
+    installed: true,
+    runnable: false,
+    command: notInstalledResult.command,
+    commandPath: null,
+    reason: "settings_found_binary_unresolved",
+    runtimeMode: notInstalledResult.runtimeMode,
+    requiresBinary: notInstalledResult.requiresBinary,
+  };
+};