docs: CLI migration design — core/go pkg/cli registry pattern

Replace manual switch/flag.FlagSet with cli.Main() + WithCommands().
6 command groups, 28 commands, full framework lifecycle.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/plans/2026-02-22-cli-migration-design.md

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+# LEM CLI Migration Design
+
+Date: 2026-02-22
+Status: Approved
+
+## Problem
+
+LEM's `main.go` is a 296-line manual `switch os.Args[1]` with `flag.FlagSet` per command. No signal handling, no shell completion, no grouped help, no framework lifecycle. The Core Go Framework provides `pkg/cli` — a full CLI SDK wrapping cobra, charmbracelet TUI, and the DI lifecycle. Every other domain repo in the fleet uses it.
+
+## Solution
+
+Replace `main.go` with `cli.Main()` + `cli.WithCommands()`. Commands register through the Core framework lifecycle. LEM gets signal handling, structured logging, shell completion, grouped help, TUI primitives (Spinner, ProgressBar, Viewport), and workspace support for free.
+
+### Single import rule
+
+LEM imports `forge.lthn.ai/core/go/pkg/cli` and **nothing else** for CLI concerns. No cobra, no lipgloss, no bubbletea. `pkg/cli` wraps everything.
+
+### New main.go (~10 lines)
+
+```go
+package main
+
+import (
+    "forge.lthn.ai/core/go/pkg/cli"
+    "forge.lthn.ai/lthn/lem/cmd/lemcmd"
+)
+
+func main() {
+    cli.Main(
+        cli.WithCommands("lem", lemcmd.AddLEMCommands),
+    )
+}
+```
+
+### Command Groups (6 groups, 28 commands)
+
+```
+lem score [score|probe|compare|tier-score|agent]         — Scoring
+lem gen [distill|expand|conv]                            — Generation
+lem data [import-all|consolidate|normalize|approve]       — Data Management
+lem export [jsonl|parquet|publish|convert]                — Export & Publish
+lem mon [status|expand-status|inventory|coverage|metrics] — Monitoring
+lem infra [ingest|seed-influx|query|worker]              — Infrastructure
+```
+
+### File Layout
+
+```
+cmd/lemcmd/
+├── lem.go          # AddLEMCommands — creates groups, registers all
+├── score.go        # score, probe, compare, tier-score, agent
+├── gen.go          # distill, expand, conv
+├── data.go         # import-all, consolidate, normalize, approve
+├── export.go       # export (renamed jsonl), parquet, publish, convert
+├── mon.go          # status, expand-status, inventory, coverage, metrics
+└── infra.go        # ingest, seed-influx, query, worker
+```
+
+### Registration Pattern
+
+Following the fleet pattern (go-ml, go-devops, cli/):
+
+```go
+// cmd/lemcmd/lem.go
+package lemcmd
+
+import "forge.lthn.ai/core/go/pkg/cli"
+
+func AddLEMCommands(root *cli.Command) {
+    addScoreCommands(root)
+    addGenCommands(root)
+    addDataCommands(root)
+    addExportCommands(root)
+    addMonCommands(root)
+    addInfraCommands(root)
+}
+```
+
+Each group file:
+
+```go
+// cmd/lemcmd/gen.go
+package lemcmd
+
+import "forge.lthn.ai/core/go/pkg/cli"
+
+func addGenCommands(root *cli.Command) {
+    genCmd := cli.NewGroup("gen", "Generation commands", "")
+
+    distillCmd := cli.NewCommand("distill", "Native Metal distillation", "", runDistill)
+    // flags via cli.StringFlag, cli.IntFlag, etc.
+
+    genCmd.AddCommand(distillCmd)
+    root.AddCommand(genCmd)
+}
+```
+
+### Phase 1: Pass-through to existing RunFoo functions
+
+Each `RunE` handler builds an `[]string` args slice from cobra flags and calls the existing `lem.RunFoo(args)` function. No business logic changes. This keeps the migration purely structural.
+
+### Phase 2 (future): Native cobra flags
+
+Migrate individual commands to use cobra flags directly instead of rebuilding `[]string`. This is optional and can be done command-by-command over time.
+
+### What changes
+
+- `main.go` shrinks from 296 lines to ~10 lines
+- `runScore()` and `runProbe()` (currently in main.go) move to `cmd/lemcmd/score.go`
+- `core/go` added as a full dependency (DI, lifecycle, signals, logging, workspace)
+- Each command gets proper `--help`, shell completion, grouped help output
+
+### What stays the same
+
+- All `pkg/lem/Run*` functions — unchanged
+- All business logic in `pkg/lem/` — untouched
+- Config loading, probe loading, scoring — unchanged
+
+### Dependencies
+
+- `forge.lthn.ai/core/go` (already in replace block, needs adding to require)
+- Transitively pulls in cobra, charmbracelet — but LEM never imports them directly