Add commit command for generating commit messages and committing

CHANGELOG.md

@@ -10,6 +10,27 @@ and the project adheres to [Semantic Versioning 2.0.0](https://semver.org/spec/v
 
 ## [Unreleased]
 
+### Added
+- **`commit` command — generate a commit message and commit (ADR-0019).**
+  `commitbrief commit` reads the staged diff, asks the configured provider for
+  a commit message, shows it for confirmation, and — on Yes (the default) or
+  `--yes` — runs `git commit`. This is the first path where the tool writes to
+  git; everything else stays read-only (PRD NG4 is rescoped to the review
+  path). Highlights:
+  - `--type` / `-t` picks the format: `plain` (default), `conventional`,
+    `conventional+body`, `gitmoji`, `subject+body`.
+  - `--generate` / `-g <N>` offers N alternatives in an arrow-key selector
+    (capped at 10); a single provider call produces all N.
+  - `--provider` / `--model` / `--cli` select the backend exactly as for a
+    review; messages are always written in English regardless of `--lang`.
+  - The pre-send `.commitbrief/**` guard, secret scan, and cost preflight all
+    run on the staged diff before the call; the suggestion is cached.
+  - With no staged changes it errors clearly; a non-TTY run without `--yes`
+    errors (it cannot confirm). `--yes` commits the first suggestion.
+  - New config keys `commit.type` and `commit.generate` set the defaults
+    (precedence: flag > config > built-in). This complements the existing
+    `--suggest-commit` review flag, which is unchanged.
+
 ### Changed
 - **`--version` no longer prints the splash logo.** `commitbrief --version`
   now emits only the single `commitbrief vX.Y.Z (commit <sha>, built <iso-ts>)`

README.md

@@ -200,6 +200,12 @@ commitbrief --unstaged --file app/Http/Controllers/API.php --file routes/web.php
 commitbrief --unstaged --dir database/seeder --dir app/Models
 commitbrief diff HEAD~3 HEAD --dir docs
 
+# Commit message (writes to git, with confirmation)
+commitbrief commit                           # suggest a message for the staged diff, then commit
+commitbrief commit --type conventional       # pick a format (-t); see "commitbrief commit" below
+commitbrief commit --generate 3              # offer 3 alternatives to choose from (-g)
+commitbrief commit --yes                     # commit the first suggestion non-interactively
+
 # Setup and rules
 commitbrief setup [--local]                  # provider + API key wizard
 commitbrief providers list|use|test          # switch active provider without re-running setup
@@ -236,6 +242,38 @@ the diff), `--no-cost-check` (skip cost preflight),
 then exit — no provider call, no cost; honours `--output`), `--color`. See
 `commitbrief --help`.
 
+### `commitbrief commit`
+
+Generate a commit message from the **staged** diff and, after you confirm,
+run `git commit`. This is the only command that writes to git — every
+review path is read-only.
+
+```sh
+commitbrief commit                          # suggest one message, confirm (default Yes), commit
+commitbrief commit -t conventional+body     # conventional subject + a generated body
+commitbrief commit -g 4                      # pick from 4 alternatives
+commitbrief commit --provider openai --model gpt-5.4-mini
+commitbrief commit --yes                     # CI/non-interactive: commit the first suggestion
+```
+
+- **`--type` / `-t`** — message format: `plain` (default), `conventional`,
+  `conventional+body`, `gitmoji`, `subject+body`.
+- **`--generate` / `-g <N>`** — produce N alternatives (1–10) and choose one
+  in an arrow-key selector. A single provider call generates all N.
+- **`--provider` / `--model` / `--cli`** — select the backend, same as a
+  review. Messages are always written in English regardless of `--lang`.
+- Defaults come from the `commit.type` and `commit.generate` config keys when
+  the flags are omitted (precedence: flag > config > built-in).
+- The pre-send `.commitbrief/**` guard, secret scan, and cost preflight run on
+  the staged diff before the call; the suggestion is cached.
+- With **nothing staged** it errors (stage with `git add` first). On a
+  **non-TTY** without `--yes` it errors, because it cannot show the confirm or
+  selector. `--yes` commits the first suggestion (it does **not** bypass the
+  secret scan or cost preflight).
+
+> The tool never auto-stages and never edits files — it only runs `git commit`
+> on changes you already staged, and only after you say Yes.
+
 ### `--with-context` (CLI providers only)
 
 By default a review sees only the diff. With `--with-context`, a
@@ -402,6 +440,9 @@ guard:
   token_preflight: false           # opt-in: confirm/abort when the prompt overflows the model's context window
 command:
   default: ""                      # args applied to a bare `commitbrief`; empty = `--staged`
+commit:
+  type: plain                      # default --type for `commitbrief commit` (plain|conventional|conventional+body|gitmoji|subject+body)
+  generate: 1                      # default --generate (number of message alternatives)
 ```
 
 ### Default command (`command.default`)

internal/cache/key.go

@@ -23,6 +23,13 @@ type ComputeArgs struct {
 	// keeping diff-only keys byte-identical to pre-ADR-0017 entries — no
 	// mass cache invalidation on upgrade.
 	WithContext bool
+
+	// Mode namespaces non-review cache entries (e.g. "commit" for the
+	// commit-message generation, ADR-0019). The commit system prompt
+	// already differs from the review prompt, so collision is unlikely;
+	// the explicit marker makes the separation impossible. Folded in only
+	// when non-empty, so review keys stay byte-identical to before.
+	Mode string
 }
 
 // Compute returns the deterministic SHA-256 key (lowercase hex) for the
@@ -46,5 +53,10 @@ func Compute(args ComputeArgs) string {
 	if args.WithContext {
 		h.Write([]byte(":ctx"))
 	}
+	// Append the mode marker only when set, so review keys stay byte-
+	// identical to before ADR-0019 (see Mode doc).
+	if args.Mode != "" {
+		h.Write([]byte(":mode:" + args.Mode))
+	}
 	return hex.EncodeToString(h.Sum(nil))
 }

internal/cli/cli_test.go

@@ -11,7 +11,7 @@ import (
 
 func TestRootCommandHasSubcommands(t *testing.T) {
 	root := newRootCmd()
-	want := []string{"cache", "compress", "config", "diff", "doctor", "dry-run", "init", "install-hook", "list", "providers", "remote", "setup"}
+	want := []string{"cache", "commit", "compress", "config", "diff", "doctor", "dry-run", "init", "install-hook", "list", "providers", "remote", "setup"}
 	got := []string{}
 	for _, c := range root.Commands() {
 		// cobra adds `help` and `completion` automatically; filter to ours.