fix(git-master): use shared shell detection for cross-platform env prefix (fix #3207)

Use detectShellType() and buildEnvPrefix() from src/shared/shell-env.ts instead of hardcoding bash-only VAR=value syntax. PowerShell users get $env:VAR='value'; cmd users get set VAR="value" &&; unix/Git Bash users keep VAR=value. Skips injecting non-bash prefixes into bash code blocks to avoid syntax mismatch.

Reland of #3214 (ekkoitac) which had unresolvable CLA + used custom shell detection instead of the shared utility.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: ekkoitac <lobster@example.com>

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/opencode-skill-loader/git-master-template-injection.ts

@@ -1,18 +1,60 @@
 import { assertValidGitEnvPrefix, type GitMasterConfig } from "../../config/schema"
+import { detectShellType, buildEnvPrefix, type ShellType } from "../../shared/shell-env"
 
 const BASH_CODE_BLOCK_PATTERN = /```bash\r?\n([\s\S]*?)```/g
 const LEADING_GIT_COMMAND_PATTERN = /^([ \t]*(?:[A-Za-z_][A-Za-z0-9_]*=[^ \t]+\s+)*)git(?=[ \t]|$)/gm
 const INLINE_GIT_COMMAND_PATTERN = /([;&|()][ \t]*)git(?=[ \t]|$)/g
 
+/**
+ * Parse a bash-format env prefix string ("VAR=value VAR2=value2") into a Record.
+ * Only handles simple KEY=VALUE pairs (no quoting needed since assertValidGitEnvPrefix
+ * already validates the format is shell-safe alphanumeric assignments).
+ */
+export function parseBashEnvPrefix(prefix: string): Record<string, string> {
+	const result: Record<string, string> = {}
+	const pairs = prefix.trim().split(/\s+/)
+	for (const pair of pairs) {
+		const eqIndex = pair.indexOf("=")
+		if (eqIndex === -1) continue
+		const key = pair.slice(0, eqIndex)
+		const value = pair.slice(eqIndex + 1)
+		result[key] = value
+	}
+	return result
+}
+
+/**
+ * Build the shell-aware command prefix for git commands.
+ * Uses the shared shell detection and env prefix builder to emit correct syntax
+ * for PowerShell ($env:VAR='value';), cmd (set VAR="value" &&), or unix (VAR=value).
+ *
+ * For unix shells, we use the inline VAR=value prefix style (not export) to match
+ * the original behavior where the env var applies only to the immediately following command.
+ */
+export function buildShellAwareGitPrefix(bashPrefix: string, shellType?: ShellType): string {
+	if (!bashPrefix) return ""
+	const resolvedShellType = shellType ?? detectShellType()
+	if (resolvedShellType === "unix" || resolvedShellType === "csh") {
+		return bashPrefix
+	}
+	const envRecord = parseBashEnvPrefix(bashPrefix)
+	return buildEnvPrefix(envRecord, resolvedShellType)
+}
+
 export function injectGitMasterConfig(template: string, config?: GitMasterConfig): string {
 	const commitFooter = config?.commit_footer ?? true
 	const includeCoAuthoredBy = config?.include_co_authored_by ?? true
 	const gitEnvPrefix = assertValidGitEnvPrefix(config?.git_env_prefix ?? "GIT_MASTER=1")
 
-	let result = gitEnvPrefix ? injectGitEnvPrefix(template, gitEnvPrefix) : template
+	const shellType = detectShellType()
+	const shellPrefix = gitEnvPrefix ? buildShellAwareGitPrefix(gitEnvPrefix, shellType) : ""
+	const codeBlockLang = shellType === "powershell" ? "pwsh" : "bash"
+	const skipBashBlockPrefixing = shellType === "powershell" || shellType === "cmd"
+
+	let result = gitEnvPrefix ? injectGitEnvPrefix(template, shellPrefix, codeBlockLang) : template
 
 	if (commitFooter || includeCoAuthoredBy) {
-		const injection = buildCommitFooterInjection(commitFooter, includeCoAuthoredBy, gitEnvPrefix)
+		const injection = buildCommitFooterInjection(commitFooter, includeCoAuthoredBy, shellPrefix)
 		const insertionPoint = result.indexOf("```\n</execution>")
 
 		result =
@@ -25,10 +67,14 @@ export function injectGitMasterConfig(template: string, config?: GitMasterConfig
 				: result + "\n\n" + injection
 	}
 
-	return gitEnvPrefix ? prefixGitCommandsInBashCodeBlocks(result, gitEnvPrefix) : result
+	if (gitEnvPrefix && !skipBashBlockPrefixing) {
+		result = prefixGitCommandsInBashCodeBlocks(result, shellPrefix)
+	}
+
+	return result
 }
 
-function injectGitEnvPrefix(template: string, prefix: string): string {
+function injectGitEnvPrefix(template: string, prefix: string, codeBlockLang: string): string {
 	const envPrefixSection = [
 		"## GIT COMMAND PREFIX (MANDATORY)",
 		"",
@@ -37,7 +83,7 @@ function injectGitEnvPrefix(template: string, prefix: string): string {
 		"",
 		"This allows custom git hooks to detect when git-master skill is active.",
 		"",
-		"```bash",
+		`\`\`\`${codeBlockLang}`,
 		`${prefix} git status`,
 		`${prefix} git add <files>`,
 		`${prefix} git commit -m "message"`,