filesystem method %q is not yet implemented in pulumi neo CL

Error message

filesystem method %q is not yet implemented in pulumi neo CLI mode

What it means

The "grep_ast" filesystem method is a known tool name but has no implementation in the pulumi neo CLI mode; the dispatcher explicitly rejects it. This is a placeholder guard for a not-yet-ported capability, not a bug in the caller's arguments.

Source

Thrown at pkg/cmd/pulumi/neo/tools/filesystem.go:182

		}
		if err := json.Unmarshal(args, &p); err != nil {
			return nil, fmt.Errorf("decoding grep args: %w", err)
		}
		return nilOnError(f.grep(p.Pattern, p.Path, p.Include))
	case "content_replace":
		var p struct {
			Pattern     string `json:"pattern"`
			Replacement string `json:"replacement"`
			Path        string `json:"path"`
			FilePattern string `json:"file_pattern,omitempty"`
			DryRun      bool   `json:"dry_run,omitempty"`
		}
		if err := json.Unmarshal(args, &p); err != nil {
			return nil, fmt.Errorf("decoding content_replace args: %w", err)
		}
		return nilOnError(f.contentReplace(ctx, p.Pattern, p.Replacement, p.Path, p.FilePattern, p.DryRun))
	case "grep_ast":
		return nil, fmt.Errorf("filesystem method %q is not yet implemented in pulumi neo CLI mode", method)
	default:
		return nil, fmt.Errorf("unknown filesystem method %q", method)
	}
}

// nilOnError drops a method's zero-valued result on the floor when it returns
// an error, so Filesystem.Invoke yields an untyped-nil `any` instead of an
// interface that wraps a zero struct. Without this Session.invokeToolCall keeps
// the empty struct as Content (a zero struct boxed into any is non-nil), and
// the agent sees IsError=true with no failure reason.
func nilOnError[T any](v T, err error) (any, error) {
	if err != nil {
		return nil, err
	}
	return v, nil
}

// resolve safely interprets a path supplied by the agent, which may be absolute or

View on GitHub (pinned to 793f7b2e16)

Solutions

Use the line-oriented "grep" method instead for regex search.
Upgrade the pulumi CLI in case a newer version implements grep_ast.
Update the agent's tool description/prompt to exclude grep_ast in CLI mode.

Example fix

// before
Invoke(ctx, "grep_ast", args)
// after
Invoke(ctx, "grep", []byte(`{"pattern":"func Name","include":"*.go"}`))

Defensive patterns

Strategy: fallback

Validate before calling

unsupportedInCLIMode := method == "grep_ast"
if unsupportedInCLIMode {
    method = "grep" // fall back to line-oriented search
}

Type guard

supported := map[string]bool{"grep": true, "content_replace": true}
_, ok := supported[method]

Try / catch

result, err := fs.Invoke(ctx, method, args)
if err != nil && strings.Contains(err.Error(), "not yet implemented") {
    result, err = fs.Invoke(ctx, "grep", args) // degrade gracefully
}

Prevention

Filter advertised tools to those implemented in the current mode.
Pin the CLI version and check release notes for new tool methods.
Document capability differences between CLI mode and upstream MCP mode.

When it happens

Trigger: Calling Filesystem.Invoke with method "grep_ast" while running the neo CLI-mode filesystem tool.

Common situations: An agent discovers tool names from upstream mcp-claude-code docs and invokes grep_ast; a prompt or tool list advertises a capability the CLI build has not implemented.

Related errors

AI-assisted analysis of pulumi/pulumi@793f7b2e16 (2026-08-31). Data as JSON: /api/errors/cb392e193dfd7744. Report an issue: GitHub.