diff --git a/CHANGELOG.md b/CHANGELOG.md
index 57b7fbaf..513131cc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@ heading, and (b) bumping `project.yaml` `version:` in the same commit.
   [ADR 0002](docs/ADRs/0002-sidecar-language-go.md) — Sidecar language: Go.
   [ADR 0003](docs/ADRs/0003-pql-as-supporter-tool.md) — pql as supporter tool; wrap, don't duplicate; pql is a Clide subsystem when present.
   [ADR 0004](docs/ADRs/0004-ignore-file-strategy.md) — Ignore file strategy (`ignore_files:` in `.pql/config.yaml`, layered).
+- Go sidecar/CLI skeleton under `sidecar/` (module `git.schweitz.net/jpmschweitzer/clide/sidecar`): `cmd/clide/main.go`, `internal/cli` with a stdlib-flag dispatch, `internal/diag` mirroring pql's exit-code + stderr-JSON contract, `internal/version` with ldflag-stamped build info, and placeholder packages for `daemon`, `pty`, `proc`, `git`, `ipc`, `pql` awaiting their tier. `clide --version` emits JSON build-info today.
 - Root `Makefile` drives both the Go sidecar and the Flutter app under one toolchain. Version is read from `project.yaml` via awk and stamped into the sidecar via `-ldflags -X`. Flutter targets gracefully noop before the app is scaffolded so the Makefile is usable from day one. Pinned Go tooling (govulncheck, goimports, golangci-lint) installs via `make tools`.
 - `ci/` entry scripts: `test.sh`, `lint.sh` (includes the supply-chain gate — no green lint without a green CVE scan), `security.sh`, `release.sh` (stub).
 - Project identity files for the Flutter rebuild at the repo root: `project.yaml` (single source of truth for version + module path, version 2.0.0-dev), a fresh `README.md`, MIT `LICENSE`, and `.editorconfig`. The Python clide's manifest and README are preserved under `legacy/`.
diff --git a/sidecar/cmd/clide/main.go b/sidecar/cmd/clide/main.go
new file mode 100644
index 00000000..129802f4
--- /dev/null
+++ b/sidecar/cmd/clide/main.go
@@ -0,0 +1,18 @@
+// Command clide is the CLI and sidecar-daemon entry point.
+//
+// One binary, two modes:
+//   - One-shot CLI (default):   clide <subcommand> [args...]
+//   - Long-running sidecar:     clide --daemon
+//
+// See docs/initial-plan.md and docs/ADRs/ for the architecture.
+package main
+
+import (
+	"os"
+
+	"git.schweitz.net/jpmschweitzer/clide/sidecar/internal/cli"
+)
+
+func main() {
+	os.Exit(cli.Run(os.Args[1:]))
+}
diff --git a/sidecar/go.mod b/sidecar/go.mod
new file mode 100644
index 00000000..0a8f2368
--- /dev/null
+++ b/sidecar/go.mod
@@ -0,0 +1,3 @@
+module git.schweitz.net/jpmschweitzer/clide/sidecar
+
+go 1.25.0
diff --git a/sidecar/internal/cli/cli.go b/sidecar/internal/cli/cli.go
new file mode 100644
index 00000000..f84ff652
--- /dev/null
+++ b/sidecar/internal/cli/cli.go
@@ -0,0 +1,53 @@
+// Package cli is the CLI front-end. cmd/clide/main.go calls Run with
+// os.Args[1:]. Subcommands land here one file per command once Tier 2
+// begins (see docs/initial-plan.md).
+//
+// Stdlib-only for the pre-Tier-0 scaffold. Cobra arrives with the first
+// real subcommand surface.
+package cli
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+
+	"git.schweitz.net/jpmschweitzer/clide/sidecar/internal/diag"
+	"git.schweitz.net/jpmschweitzer/clide/sidecar/internal/version"
+)
+
+// Run dispatches CLI args. Returns the process exit code per the diag
+// contract.
+func Run(args []string) int {
+	fs := flag.NewFlagSet("clide", flag.ContinueOnError)
+	fs.SetOutput(os.Stderr)
+
+	daemon := fs.Bool("daemon", false, "run as the long-running sidecar daemon")
+	showVersion := fs.Bool("version", false, "print build info and exit")
+
+	if err := fs.Parse(args); err != nil {
+		return diag.Usage
+	}
+
+	if *showVersion {
+		b, _ := json.Marshal(version.Info())
+		fmt.Println(string(b))
+		return diag.OK
+	}
+
+	if *daemon {
+		diag.Error("cli.not-implemented", "daemon mode not yet implemented", "tier 0 — sidecar scaffold lands next")
+		return diag.Software
+	}
+
+	// No subcommand yet. Surface the pql-style exit 64 so callers can tell
+	// the difference between "no instructions" and a successful run.
+	rest := fs.Args()
+	if len(rest) == 0 {
+		diag.Error("cli.usage", "no subcommand given", "see docs/initial-plan.md — Tier 2 defines the CLI surface")
+		return diag.Usage
+	}
+
+	diag.Error("cli.not-implemented", fmt.Sprintf("subcommand %q not yet implemented", rest[0]), "tier 2 lands the CLI surface")
+	return diag.Software
+}
diff --git a/sidecar/internal/daemon/doc.go b/sidecar/internal/daemon/doc.go
new file mode 100644
index 00000000..154958c7
--- /dev/null
+++ b/sidecar/internal/daemon/doc.go
@@ -0,0 +1,7 @@
+// Package daemon hosts the --daemon-mode entry point: lifecycle
+// management (socket binding, token-auth setup, single-instance lock,
+// graceful shutdown), subsystem wiring (pty, proc, git, pql, ipc), and
+// the long-lived event loop.
+//
+// Empty for now — lands in Tier 0.
+package daemon
diff --git a/sidecar/internal/diag/diag.go b/sidecar/internal/diag/diag.go
new file mode 100644
index 00000000..85544777
--- /dev/null
+++ b/sidecar/internal/diag/diag.go
@@ -0,0 +1,58 @@
+// Package diag defines the exit-code contract and emits structured
+// diagnostics to stderr as line-delimited JSON.
+//
+// Mirrors pql's diag contract so Claude (and any other tool that
+// consumes both CLIs) sees a single shape.
+package diag
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+// Exit codes. Same numeric space as pql's.
+const (
+	OK       = 0  // success
+	NoMatch  = 2  // success with zero matches / nothing to do
+	Usage    = 64 // EX_USAGE — bad CLI flag or missing subcommand
+	DataErr  = 65 // EX_DATAERR — malformed request
+	NoInput  = 66 // EX_NOINPUT — missing required resource (repo, socket, file)
+	Unavail  = 69 // EX_UNAVAILABLE — sidecar unreachable / subsystem down
+	Software = 70 // EX_SOFTWARE — internal error
+)
+
+type Level string
+
+const (
+	LevelWarn  Level = "warn"
+	LevelError Level = "error"
+)
+
+// Diagnostic is one entry in the stderr JSON-per-line stream.
+type Diagnostic struct {
+	Level Level  `json:"level"`
+	Code  string `json:"code"`
+	Msg   string `json:"msg"`
+	Hint  string `json:"hint,omitempty"`
+}
+
+// Emit writes a diagnostic as one JSON line to w.
+func Emit(w io.Writer, d Diagnostic) {
+	b, err := json.Marshal(d)
+	if err != nil {
+		_, _ = io.WriteString(w, `{"level":"error","code":"diag.marshal","msg":"failed to marshal diagnostic"}`+"\n")
+		return
+	}
+	_, _ = w.Write(append(b, '\n'))
+}
+
+// Warn emits a warning diagnostic to stderr.
+func Warn(code, msg string) {
+	Emit(os.Stderr, Diagnostic{Level: LevelWarn, Code: code, Msg: msg})
+}
+
+// Error emits an error diagnostic to stderr.
+func Error(code, msg, hint string) {
+	Emit(os.Stderr, Diagnostic{Level: LevelError, Code: code, Msg: msg, Hint: hint})
+}
diff --git a/sidecar/internal/git/doc.go b/sidecar/internal/git/doc.go
new file mode 100644
index 00000000..fe58bacd
--- /dev/null
+++ b/sidecar/internal/git/doc.go
@@ -0,0 +1,5 @@
+// Package git shells out to git for the Git panel, diff rendering, and
+// the `clide git <subcommand>` CLI surface.
+//
+// Empty for now — lands in Tier 3.
+package git
diff --git a/sidecar/internal/ipc/doc.go b/sidecar/internal/ipc/doc.go
new file mode 100644
index 00000000..4760aa80
--- /dev/null
+++ b/sidecar/internal/ipc/doc.go
@@ -0,0 +1,6 @@
+// Package ipc hosts the unix-socket JSON-lines server the sidecar
+// exposes to the Flutter app and CLI. Token-authenticated; dispatches
+// to the pty, proc, git, pql, canvas, and pane subsystems.
+//
+// Empty for now — lands in Tier 0.
+package ipc
diff --git a/sidecar/internal/pql/doc.go b/sidecar/internal/pql/doc.go
new file mode 100644
index 00000000..f4ab5eab
--- /dev/null
+++ b/sidecar/internal/pql/doc.go
@@ -0,0 +1,10 @@
+// Package pql is the *only* place Clide contains pql logic. Pure
+// shell-outs to the `pql` binary — no re-implementation of pql's
+// indexer, ranker, or frontmatter parsing.
+//
+// See docs/ADRs/0003-pql-as-supporter-tool.md for the wrap-don't-
+// duplicate rule and the "pql is a Clide subsystem when present"
+// invariant.
+//
+// Empty for now — lands in Tier 4.
+package pql
diff --git a/sidecar/internal/proc/doc.go b/sidecar/internal/proc/doc.go
new file mode 100644
index 00000000..c0b2092c
--- /dev/null
+++ b/sidecar/internal/proc/doc.go
@@ -0,0 +1,6 @@
+// Package proc manages subprocess lifecycles spawned by the sidecar —
+// git operations, pql invocations, and anything else the app or CLI
+// requests.
+//
+// Empty for now — lands alongside Tier 1/3 subsystems.
+package proc
diff --git a/sidecar/internal/pty/doc.go b/sidecar/internal/pty/doc.go
new file mode 100644
index 00000000..557f55ec
--- /dev/null
+++ b/sidecar/internal/pty/doc.go
@@ -0,0 +1,6 @@
+// Package pty owns the PTY lifecycle for terminals hosted inside the
+// sidecar daemon. Drives xterm.dart panes in the Flutter app and the
+// `clide` CLI's direct-attach mode.
+//
+// Empty for now — lands in Tier 1.
+package pty
diff --git a/sidecar/internal/version/version.go b/sidecar/internal/version/version.go
new file mode 100644
index 00000000..605b1661
--- /dev/null
+++ b/sidecar/internal/version/version.go
@@ -0,0 +1,35 @@
+// Package version exposes build-info stamped via -ldflags at build time.
+// See the root Makefile's LDFLAGS for the -X targets.
+package version
+
+import "runtime"
+
+var (
+	Version = "dev"
+	Commit  = "unknown"
+	Date    = "unknown"
+)
+
+// SchemaVersion tracks the app↔sidecar IPC contract. Bump when the wire
+// format changes in a way that requires coordinated app and sidecar
+// updates. Mirror in project.yaml `schema_version:` when that field is
+// added there.
+const SchemaVersion = 0
+
+type BuildInfo struct {
+	Version       string `json:"version"`
+	Commit        string `json:"commit"`
+	Date          string `json:"date"`
+	GoVersion     string `json:"go_version"`
+	SchemaVersion int    `json:"schema_version"`
+}
+
+func Info() BuildInfo {
+	return BuildInfo{
+		Version:       Version,
+		Commit:        Commit,
+		Date:          Date,
+		GoVersion:     runtime.Version(),
+		SchemaVersion: SchemaVersion,
+	}
+}