diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index c33946b..0141d88 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -39,7 +39,7 @@ repos:
           name: commit message is valid
           args:
             - --negate
-          entry: ^(build|ci|docs|feat|fix|perf|refactor|style|test|revert|hotfix|ops|chore)\([\w,\.,\-,\(,\),\/]+\)(!?)(:)\s{1}([\w,\W,:]+)$
+          entry: ^(build|ci|docs|feat|fix|perf|refactor|style|test|revert|hotfix|ops|chore|incompat)\([\w,\.,\-,\(,\),\/]+\)(!?)(:)\s{1}([\w,\W,:]+)$
           language: pygrep
           stages:
             - commit-msg
diff --git a/Cargo.toml b/Cargo.toml
index f137a36..44ba440 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,6 +15,7 @@ include = [
   "/Cargo.lock",
   "/LICENSE",
   "/README.md",
+  "/docs/compatibility.md",
 ]
 
 [[bin]]
diff --git a/README.md b/README.md
index 7f2a33a..e371d5d 100644
--- a/README.md
+++ b/README.md
@@ -5,6 +5,10 @@ named aliases and mounts, Git-aware shortcuts, optional zoxide resolution, and a
 fzf worktree jump while leaving the final directory change to your shell's real
 `cd` builtin.
 
+Starting with 1.0.0, documented commands, configuration, shell behavior, and JSON
+output follow the [v1 compatibility contract](docs/compatibility.md). That contract
+also describes how to upgrade generated shell integration and consume output in scripts.
+
 ## Install
 
 ### Homebrew
diff --git a/docs/compatibility.md b/docs/compatibility.md
new file mode 100644
index 0000000..3657740
--- /dev/null
+++ b/docs/compatibility.md
@@ -0,0 +1,126 @@
+# Compatibility from 1.0.0
+
+This contract applies starting with cj 1.0.0. Throughout 1.x, existing documented
+commands and valid configuration retain their meaning. New features can be added,
+and bugs can be corrected to match the documented behavior. An incompatible change
+to the public contract requires a major release and migration notes, following
+[Semantic Versioning](https://semver.org/).
+
+## Public commands and configuration
+
+The public interface consists of the commands and flags in `cj --help` and the
+usage documented in the [README](../README.md). This includes their accepted
+arguments, resolver controls, and the distinction between printing a destination
+with `cj` and changing the parent shell's directory with the generated `cd` wrapper.
+Documented aliases such as `pwsh` and the compatibility flag
+`--setup-key-binding` remain accepted throughout 1.x.
+
+Existing documented TOML sections, field names, accepted values, and defaults remain
+supported. This includes configuration path selection, the legacy string form of
+key bindings, and the legacy `one-drive` spelling for the `onedrive` provider.
+New optional settings may be added. Unknown fields are rejected, so a configuration
+using a new setting may require the version that introduced it; compatibility does
+not mean that older binaries understand newer settings.
+
+For ordinary resolution, existing directories take precedence over navigation
+tickers, aliases, mounts, and Git keywords, in that order. The configured resolver
+then supplies zoxide or literal-path fallback. Explicit `-r`, `-z`, and `-Z` modes
+keep their documented overrides. A configured alias or mount that cannot be reached
+remains an error rather than silently resolving to another destination.
+
+## Generated shell integration
+
+The documented `cd` wrapper, directory history, Tab completion, and optional key
+binding behavior are public across Bash, Zsh, Nushell, and PowerShell, subject to
+the shell requirements in the README. Completion inserts a candidate; execution
+performs the directory change. Native shell escapes bypass cj's history tracking.
+
+In particular, bare `cd -jw` and `cd --jump-worktree` jump to the primary worktree,
+regardless of the branch checked out there. Tab, with or without a preceding
+space, offers worktree candidates. Standalone `cj -jw` remains an fzf picker that
+prints the selected path. These operations do not switch Git branches.
+
+After upgrading the binary, regenerate both `cj init <shell>` and
+`cj completions <shell>` output using that binary and your chosen `-C` configuration,
+then reload them in the matching shell or restart it. The README contains the
+commands for each shell. Also regenerate after changing settings captured in the
+generated files, such as tickers, key bindings, or completion names. Reloading the
+integration resets the session's directory history.
+
+Generated files and the binary are a matched pair. Their source text, helper
+function names, private variables, and internal protocols may change within 1.x.
+Do not call those helpers directly, edit the generated files as an extension API,
+or rely on mixing files from one version with a different binary.
+
+## Output for scripts
+
+A successful destination-resolution command writes the path followed by one LF
+to stdout. The path is data, not shell code: it is not shell-quoted and can be
+relative. Quote it when passing it to the shell's directory command. On Unix,
+path output can contain non-UTF-8 bytes and embedded or trailing newlines; remove
+only the final output LF when preserving the exact path.
+
+Cancelling the standalone worktree picker, or getting no match, succeeds with an
+empty selection (one output LF). Check that a destination was returned before
+changing directory. A successful resolution alone does not guarantee that a
+literal fallback path exists; the shell performs the directory change.
+
+Scripts may rely on exit status zero for success and nonzero for failure, and on
+diagnostics going to stderr rather than being mixed into path or JSON output.
+Exact diagnostic wording and individual nonzero status values are not stable APIs.
+
+Use `--format json` for worktree listings and mount discovery. Existing fields,
+their types, nullability, and meanings are stable. Consumers must ignore unknown
+fields, tolerate new `source` and `status` strings, and avoid depending on JSON
+whitespace, object key order, or array order.
+
+### Worktree JSON
+
+`cj --worktree --format json` returns an array of objects:
+
+| Fields | Type and meaning |
+| --- | --- |
+| `path` | String containing the worktree path; `--relative` makes it relative to the current directory when possible. |
+| `branch`, `head` | Branch name without `refs/heads/`, and full commit ID; each is a string or `null` when absent. |
+| `main`, `bare`, `detached`, `locked`, `prunable` | Boolean state flags. `main` identifies the primary worktree, not a branch named `main`. |
+| `lock_reason`, `prune_reason` | String or `null`; a true state flag can have no reason. |
+
+Worktree JSON requires Unicode paths; an unrepresentable path is an error rather
+than a silently changed destination. Path separators and absolute path syntax
+follow the platform, so compare paths using platform-aware operations.
+
+### Mount scan JSON
+
+`cj mounts scan --format json` returns an object with these arrays:
+
+| Field | Entries |
+| --- | --- |
+| `mounts` | Objects with string fields `name`, `source`, and `path` for ready mounts. |
+| `skipped` | Objects with string fields `name`, `source`, `status`, and `reason`. With `--verbose`, each also includes `candidates`, an array of path strings. |
+| `warnings` | Diagnostic strings. |
+
+The text in `reason` and `warnings` is for people and can change; use structural
+fields for automation. Discovered paths and the set of available mounts depend on
+the current machine and connected storage.
+
+## Outside the public contract
+
+Human-readable tables, help layout, picker appearance, completion ordering, and
+exact generated source can evolve within 1.x. Undocumented flags (including
+`--internal-*`), `CJ_INTERNAL_*` environment variables, and generated helper names
+are private implementation details. Rust modules are internal to the executable;
+the package does not promise a Rust library API.
+
+## Release convention
+
+This repository uses the `incompat` commit type to request a major release, `feat`
+for a minor release, and `fix` for a patch release. Every intentional incompatible
+public change must use `incompat: ...` or `incompat(scope): ...` and explain the
+migration. The commit-message hook requires the scoped form, for example
+`incompat(release): establish the v1 compatibility contract`. It is a commit type,
+not a scope on `feat` or `fix`.
+
+The current release rules map a breaking-change marker alone to a minor release;
+`!` or a `BREAKING CHANGE` footer therefore does not replace the required
+`incompat` type. The first v1 contract commit uses `incompat` to request 1.0.0.
+Version files and tags are produced by the maintainer-triggered release workflow.