Release 2.2.0 — unified onboard strategy + safety hardening

Folds `josh-sync adopt` into `josh-sync onboard <target>` as the adopt
strategy alongside the original reset flow. Strategy resolves by
precedence: --mode flag > targets[].history_lock config (preserve|rewrite)
> auto-detect via `git ls-remote --heads`. `josh-sync adopt` is kept as
a thin alias. Adds the new `targets[].history_lock` config field
(validated at parse time) and folds `<target>/adopt.json` state into
`<target>/onboard.json` with a `.strategy` field; legacy state files
are read with a backward-compat fallback.

Safety hardening (from a multi-angle review of the unification):
- auto-detect distinguishes auth/network failure from empty repo
- resume validates --mode against the strategy saved in state
- `josh-sync adopt` rejects a conflicting --mode in the forwarded args
- missing import-PR lookup dies in both strategies (was WARN+continue
  for reset, which could create duplicate import PRs on resume)
- --restart durably removes the legacy adopt.json from the state branch
- adopt_branch is now a subshell function (EXIT trap can't clobber callers)
- strategy value validated after resolve/load (reset|adopt)
- --mode with missing/empty value dies with a usage hint
- migrate-pr against an adopt-strategy target dies with a specific hint
- reset importing asserts archived_url is present (no "null" → git clone)

End-to-end + CLI bats coverage added (tests/unit/adopt_e2e.bats,
tests/unit/cli.bats). 72 tests, shellcheck clean.

Makefile dist bundle header now correctly interpolates VERSION and
line count.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/guide.md

@@ -222,20 +222,31 @@ This validates:
 
 For a new monorepo before import, preflight may warn that subfolders don't exist yet — that's expected.
 
-## Step 5: Import Existing Subrepos
+## Step 5: Onboard Existing Subrepos
 
-This is the critical onboarding step. There are three approaches:
+`josh-sync onboard <target>` is the single entry point for connecting an existing subrepo to the monorepo. It runs interactively with checkpoint/resume and picks one of two strategies:
 
-- **`josh-sync adopt`** (recommended for active existing subrepos) — non-destructive, resumable, preserves existing subrepo history
-- **`josh-sync onboard`** — destructive replacement-repo workflow for teams that intentionally archive the old repo
-- **Manual `import` → merge → `reset`** — lower-level destructive path for automation or empty replacement repos
+- **adopt** (non-destructive) — keeps the subrepo's existing history and joins it to josh-filtered history via a single adoption merge commit. No force-push. Developers fast-forward; open PR branches stay valid.
+- **reset** (destructive) — force-pushes josh-filtered history onto the subrepo, replacing its prior history. Use this for empty replacement repos (typically paired with renaming the old repo to `*-archived`).
 
-### Option A: Adopt (recommended for active subrepos)
+### Strategy selection
 
-Use `adopt` when the subrepo already exists, developers already clone it, or open PR branches should remain based on existing history.
+`josh-sync onboard` resolves the strategy in this order (highest precedence first):
+
+1. **CLI flag** — `--mode=adopt` or `--mode=reset` overrides everything.
+2. **Config** — `targets[].history_lock: preserve` selects adopt; `rewrite` selects reset.
+3. **Auto-detect** — `git ls-remote --heads` on the subrepo. Branches present → adopt. Empty repo → reset.
+
+The chosen strategy is logged at preflight so you can see what will happen before any side effects.
+
+`josh-sync adopt <target>` is kept as a back-compat alias for `josh-sync onboard --mode=adopt`.
+
+### Adopt strategy (auto-selected for active subrepos)
 
 ```bash
-josh-sync adopt billing
+josh-sync onboard billing                # auto-detect — picks adopt for non-empty subrepo
+josh-sync onboard billing --mode=adopt   # force adopt explicitly
+josh-sync adopt billing                  # equivalent back-compat alias
 ```
 
 The command will:
@@ -245,7 +256,7 @@ The command will:
 4. **Adopt** — creates a merge commit on the subrepo with Josh-filtered HEAD as parent 1 and existing subrepo HEAD as parent 2
 5. **Push** — pushes the adoption merge with a normal fast-forward push, never force-push
 
-The adoption merge preserves the old subrepo history while giving Josh a first-parent path back to the monorepo. If interrupted, re-run `josh-sync adopt billing` to resume. Use `--restart` to start over.
+The adoption merge preserves the old subrepo history while giving Josh a first-parent path back to the monorepo. If interrupted, re-run `josh-sync onboard billing` to resume. Use `--restart` to start over. See [ADR-013](adr/013-non-destructive-adoption.md) for the design rationale.
 
 After adoption, developers can update existing clones with a normal fast-forward:
 
@@ -255,9 +266,9 @@ git checkout main
 git merge --ff-only origin/main
 ```
 
-### Option B: Onboard with replacement repo
+### Reset strategy (auto-selected for empty replacement repos)
 
-The `onboard` command walks through the destructive replacement-repo process interactively, with checkpoint/resume at every step.
+Use the reset strategy when you intentionally want to archive the old subrepo and start fresh from a new empty repo.
 
 **Before you start:**
 
@@ -269,7 +280,8 @@ The rename preserves the archived repo with all its history and open PRs. The ne
 **Run onboard:**
 
 ```bash
-josh-sync onboard billing
+josh-sync onboard billing                # auto-detect — picks reset for empty subrepo
+josh-sync onboard billing --mode=reset   # force reset explicitly
 ```
 
 The command will:
@@ -298,13 +310,13 @@ josh-sync migrate-pr billing 5 8 12
 
 PR migration works by fetching the diff from the archived repo's PR, applying it to the new repo, and creating a new PR. File content is identical after reset, so patches apply cleanly.
 
-### Option C: Manual import → merge → reset
+### Manual: import → merge → reset
 
-Use this for scripted automation or when you intentionally want to replace subrepo history.
+Use this for scripted automation or when you intentionally want to replace subrepo history without the interactive wrapper.
 
 > Do this **one target at a time** to keep PRs reviewable.
 
-#### 5c-1. Import
+#### Manual: Import
 
 ```bash
 josh-sync import billing
@@ -319,13 +331,13 @@ This:
 
 Review the import PR — check for leaked credentials, environment-specific config, or files that shouldn't be in the monorepo.
 
-#### 5c-2. Merge the import PR
+#### Manual: Merge the import PR
 
 Merge the PR using your Git platform's UI. This lands the subrepo content into the monorepo's main branch.
 
 > At this point, the monorepo has the content but the histories are disconnected. Sync will **not** work until you complete the reset step.
 
-#### 5c-3. Reset
+#### Manual: Reset
 
 ```bash
 josh-sync reset billing
@@ -352,7 +364,7 @@ git checkout stage && git reset --hard origin/stage   # repeat for each branch
 
 Or simply delete and re-clone the subrepo. Local-only branches (not pushed to the remote) will be lost either way.
 
-#### 5c-4. Repeat for each target
+#### Manual: Repeat for each target
 
 ```
 For each target:
@@ -646,15 +658,13 @@ To add a new subrepo after initial setup:
 1. Add the target to `.josh-sync.yml`
 2. Update the forward workflow's `paths:` list to include the new subfolder
 3. Commit and push
-4. Import or adopt the target:
+4. Onboard the target — `josh-sync onboard` auto-picks `adopt` for non-empty subrepos and `reset` for empty ones; override with `--mode={reset,adopt}` or pin via the target's `history_lock` config field.
    ```bash
-   # Recommended for an existing active subrepo
-   josh-sync adopt new-target
+   josh-sync onboard new-target                # auto-detect strategy
+   josh-sync onboard new-target --mode=adopt   # force adopt
+   josh-sync onboard new-target --mode=reset   # force reset
 
-   # Replacement-repo workflow
-   josh-sync onboard new-target
-
-   # Or manual: import → merge PR → reset
+   # Manual lower-level path (when scripting):
    josh-sync import new-target
    # merge the PR
    josh-sync reset new-target