diff --git a/Brewfile b/Brewfile
index 97fa1ef..d8f6b8e 100644
--- a/Brewfile
+++ b/Brewfile
@@ -18,6 +18,7 @@ brew "pyenv"
 brew "tmux"
 brew "tree"
 brew "wget"
+brew "yq"
 brew "zsh-autosuggestions"
 brew "zsh-syntax-highlighting"
 cask "font-hack-nerd-font"
diff --git a/README.md b/README.md
index 49af985..022b899 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,44 @@ cd into the `dotfiles` directory, and then run:
 ./assimilate.sh
 ```
 
+The installer shares `agent-instructions.md` with Claude Code and Codex by
+linking it to `~/.claude/CLAUDE.md` and `~/.codex/AGENTS.md`.
+
+### Codex configuration
+
+`assimilate.sh` uses `yq` to structurally merge the portable root settings from
+`codex/config.managed.toml` into `~/.codex/config.toml`. It validates the merged
+file with Codex's strict config loader before replacing the live config
+atomically. Settings outside the managed fragment are preserved, and the first
+existing config is retained as `~/.codex/config.toml.dotfiles-backup`.
+
+The checked-in settings enable turn notifications, automatic review, low
+verbosity, concise reasoning summaries, and the pragmatic personality. Codex
+uses `AGENTS.md` natively and falls back to `CLAUDE.md` when it is absent.
+
+Enable continuous Claude Code import once in the Codex UI and leave session
+imports disabled. Those choices are desktop-local state and are deliberately
+not automated through internal state files or JSON-RPC APIs.
+
+The portable Git preferences—branch prefix, squash merge method, and PR and
+commit instructions—are managed in the schema-supported `[desktop]` table.
+Other desktop preferences such as appearance, editor target, and queue behavior
+remain local. Generated and machine-specific state such as local paths,
+installed plugins, connector authentication, caches, session history, and
+per-project trust also remains local. Never check in
+`.codex-global-state.json`, Codex session databases, or the complete live
+`config.toml`.
+
+### Claude Code configuration
+
+`assimilate.sh` uses `jq` to structurally merge the portable settings from
+`claude/settings.managed.json` into `~/.claude/settings.json`. Local settings
+such as permissions, hooks, plugins, and model selection are preserved. The
+managed fragment enables concise output, configures the checked-in statusline,
+and disables commit attribution, PR attribution, and cloud or Remote Control
+session links. The first existing settings file is retained as
+`~/.claude/settings.json.dotfiles-backup`.
+
 ### Tmux Plugin Manager
 - Install Tmux Plugin Manager ([Github](https://github.com/tmux-plugins/tpm#tmux-plugin-manager))
 - Install tmux packages with `prefix + I`
diff --git a/agent-instructions.md b/agent-instructions.md
new file mode 100644
index 0000000..08a891e
--- /dev/null
+++ b/agent-instructions.md
@@ -0,0 +1,19 @@
+# Commit Instructions
+
+Commit messages should be concise, just one sentence
+
+# Pull Request Instructions
+
+Create pull requests with the simple format
+
+## Summary
+<Describe the context for your change>
+
+## Test Plan
+<Evidence that the PR is working, include screenshots, and the CLI commands that you ran>
+
+# Code Formatting Instructions
+
+Single-line commands or code within a sentence should be wrapped in backticks
+
+Multi-line commands or code should use fenced code blocks with triple backticks
diff --git a/assimilate.sh b/assimilate.sh
index e445ec1..336b923 100755
--- a/assimilate.sh
+++ b/assimilate.sh
@@ -3,7 +3,7 @@
 set -ex
 
 PREFIX="$HOME"
-DOTFILES="$PREFIX/dotfiles"
+DOTFILES=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
 BACKUPS="$PREFIX/backups"
 
 function sym () {
@@ -44,10 +44,15 @@ sym ghostty/config      Library/Application\ Support/com.mitchellh.ghostty/confi
 sym tmux-powerline/config.sh   .config/tmux-powerline/config.sh
 sym tmux-powerline/themes/theme.sh  .config/tmux-powerline/themes/theme.sh
 sym claude/statusline.sh .claude/statusline.sh
+sym agent-instructions.md .claude/CLAUDE.md
+sym agent-instructions.md .codex/AGENTS.md
 sym zed/keymap.json     .config/zed/keymap.json
 
 brew bundle install
 
+"$DOTFILES/claude/sync-settings.sh"
+"$DOTFILES/codex/sync-config.sh"
+
 function clone_pinned () {
   url="$1"; dir="$2"; sha="$3"
   if [ ! -d "$dir" ]; then
diff --git a/claude/settings.managed.json b/claude/settings.managed.json
new file mode 100644
index 0000000..b94cf63
--- /dev/null
+++ b/claude/settings.managed.json
@@ -0,0 +1,14 @@
+{
+  "$schema": "https://json.schemastore.org/claude-code-settings.json",
+  "attribution": {
+    "commit": "",
+    "pr": "",
+    "sessionUrl": false
+  },
+  "outputStyle": "Concise",
+  "statusLine": {
+    "type": "command",
+    "command": "~/.claude/statusline.sh",
+    "padding": 0
+  }
+}
diff --git a/claude/sync-settings.sh b/claude/sync-settings.sh
new file mode 100755
index 0000000..26a832f
--- /dev/null
+++ b/claude/sync-settings.sh
@@ -0,0 +1,41 @@
+#!/usr/bin/env sh
+
+set -eu
+
+script_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+managed_settings="$script_dir/settings.managed.json"
+claude_home=${CLAUDE_CONFIG_DIR:-"$HOME/.claude"}
+dest_settings="$claude_home/settings.json"
+backup_settings="$claude_home/settings.json.dotfiles-backup"
+
+if ! command -v jq >/dev/null 2>&1; then
+  echo "error: jq is required to sync Claude settings" >&2
+  exit 1
+fi
+
+mkdir -p "$claude_home"
+tmp_settings=$(mktemp "$claude_home/.settings.json.XXXXXX")
+
+cleanup() {
+  rm -f "$tmp_settings"
+}
+trap cleanup EXIT HUP INT TERM
+
+if [ -f "$dest_settings" ]; then
+  jq -s '.[0] * .[1]' "$dest_settings" "$managed_settings" > "$tmp_settings"
+else
+  jq '.' "$managed_settings" > "$tmp_settings"
+fi
+
+jq -e 'type == "object"' "$tmp_settings" >/dev/null
+chmod 600 "$tmp_settings"
+
+if [ -f "$dest_settings" ] && [ ! -f "$backup_settings" ]; then
+  cp -p "$dest_settings" "$backup_settings"
+  chmod 600 "$backup_settings"
+fi
+
+mv "$tmp_settings" "$dest_settings"
+tmp_settings=
+
+echo "> Synced managed Claude settings to $dest_settings"
diff --git a/codex/config.managed.toml b/codex/config.managed.toml
new file mode 100644
index 0000000..2648f26
--- /dev/null
+++ b/codex/config.managed.toml
@@ -0,0 +1,23 @@
+#:schema https://developers.openai.com/codex/config-schema.json
+
+notify = ["/bin/sh", "-c", "/usr/bin/osascript -e 'display notification \"Turn completed\" with title \"Codex\"' >/dev/null 2>&1"]
+model_reasoning_summary = "concise"
+model_verbosity = "low"
+personality = "pragmatic"
+approvals_reviewer = "auto_review"
+
+# AGENTS.md is built in; use CLAUDE.md when no AGENTS.md is present.
+project_doc_fallback_filenames = ["CLAUDE.md"]
+project_doc_max_bytes = 196608
+
+[desktop]
+git-branch-prefix = "akan72/"
+git-pull-request-merge-method = "squash"
+git-commit-instructions = "Commit messages should be concise, just one sentence"
+git-pr-instructions = """Create pull requests with the simple format
+
+## Summary
+<Describe the context for your change>
+
+## Test Plan
+<Evidence that the PR is working, include screenshots, and the CLI commands that you ran>"""
diff --git a/codex/sync-config.sh b/codex/sync-config.sh
new file mode 100755
index 0000000..5423ec0
--- /dev/null
+++ b/codex/sync-config.sh
@@ -0,0 +1,59 @@
+#!/usr/bin/env sh
+
+set -eu
+
+script_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+managed_config="$script_dir/config.managed.toml"
+codex_home=${CODEX_HOME:-"$HOME/.codex"}
+dest_config="$codex_home/config.toml"
+backup_config="$codex_home/config.toml.dotfiles-backup"
+
+if ! command -v yq >/dev/null 2>&1; then
+  echo "error: yq is required to sync Codex settings" >&2
+  exit 1
+fi
+
+if ! command -v codex >/dev/null 2>&1; then
+  echo "error: codex is required to validate Codex settings" >&2
+  exit 1
+fi
+
+mkdir -p "$codex_home"
+tmp_config=$(mktemp "$codex_home/.config.toml.XXXXXX")
+validation_home=$(mktemp -d "${TMPDIR:-/tmp}/codex-config-validation.XXXXXX")
+
+cleanup() {
+  rm -f "$tmp_config"
+  rm -rf "$validation_home"
+}
+trap cleanup EXIT HUP INT TERM
+
+if [ -f "$dest_config" ]; then
+  yq eval-all \
+    --input-format=toml \
+    --output-format=toml \
+    'select(fileIndex == 0) * select(fileIndex == 1)' \
+    "$dest_config" "$managed_config" > "$tmp_config"
+else
+  cp "$managed_config" "$tmp_config"
+fi
+
+chmod 600 "$tmp_config"
+cp "$tmp_config" "$validation_home/config.toml"
+validation_log="$validation_home/stderr.log"
+if ! CODEX_HOME="$validation_home" \
+  codex app-server --strict-config --listen stdio:// \
+    </dev/null >/dev/null 2>"$validation_log"; then
+  cat "$validation_log" >&2
+  exit 1
+fi
+
+if [ -f "$dest_config" ] && [ ! -f "$backup_config" ]; then
+  cp -p "$dest_config" "$backup_config"
+  chmod 600 "$backup_config"
+fi
+
+mv "$tmp_config" "$dest_config"
+tmp_config=
+
+echo "> Synced managed Codex settings to $dest_config"
diff --git a/tests/assimilate-path.sh b/tests/assimilate-path.sh
new file mode 100755
index 0000000..1a222aa
--- /dev/null
+++ b/tests/assimilate-path.sh
@@ -0,0 +1,47 @@
+#!/usr/bin/env sh
+
+set -eu
+
+test_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+repo_root=$(CDPATH= cd -- "$test_dir/.." && pwd)
+test_home=$(mktemp -d "${TMPDIR:-/tmp}/assimilate-path.XXXXXX")
+codex_marker="$test_home/codex-called"
+
+cleanup() {
+  rm -rf "$test_home"
+}
+trap cleanup EXIT HUP INT TERM
+
+set +e
+HOME="$test_home" \
+  PATH="$test_dir/fixtures/bin:$PATH" \
+  TEST_CODEX_MARKER="$codex_marker" \
+  sh "$repo_root/assimilate.sh" >/dev/null 2>&1
+status=$?
+set -e
+
+if [ "$status" -ne 1 ]; then
+  echo "expected assimilate.sh to reach the stubbed codex command, got status $status" >&2
+  exit 1
+fi
+
+if [ ! -f "$codex_marker" ]; then
+  echo "expected the checkout's Codex sync script to invoke codex" >&2
+  exit 1
+fi
+
+test "$(readlink "$test_home/.claude/CLAUDE.md")" = "$repo_root/agent-instructions.md"
+test "$(readlink "$test_home/.codex/AGENTS.md")" = "$repo_root/agent-instructions.md"
+test "$(readlink "$test_home/.claude/statusline.sh")" = "$repo_root/claude/statusline.sh"
+test -f "$test_home/.claude/settings.json"
+test ! -L "$test_home/.claude/settings.json"
+test "$(jq -r '.outputStyle' "$test_home/.claude/settings.json")" = "Concise"
+
+expected_args='app-server --strict-config --listen stdio://'
+actual_args=$(sed -n '1p' "$codex_marker")
+if [ "$actual_args" != "$expected_args" ]; then
+  echo "expected Codex validator arguments $expected_args, got $actual_args" >&2
+  exit 1
+fi
+
+echo "assimilate.sh resolves files relative to its own checkout"
diff --git a/tests/claude-sync-settings.sh b/tests/claude-sync-settings.sh
new file mode 100755
index 0000000..6822d34
--- /dev/null
+++ b/tests/claude-sync-settings.sh
@@ -0,0 +1,57 @@
+#!/usr/bin/env sh
+
+set -eu
+
+test_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+repo_root=$(CDPATH= cd -- "$test_dir/.." && pwd)
+test_root=$(mktemp -d "${TMPDIR:-/tmp}/claude-sync.XXXXXX")
+claude_home="$test_root/claude-home"
+invalid_home="$test_root/invalid-home"
+
+cleanup() {
+  rm -rf "$test_root"
+}
+trap cleanup EXIT HUP INT TERM
+
+mkdir -p "$claude_home" "$invalid_home"
+cp "$test_dir/fixtures/claude/settings.json" "$claude_home/settings.json"
+cp "$test_dir/fixtures/claude/invalid-settings.json" "$invalid_home/settings.json"
+
+original_hash=$(shasum -a 256 "$claude_home/settings.json" | awk '{print $1}')
+CLAUDE_CONFIG_DIR="$claude_home" "$repo_root/claude/sync-settings.sh"
+
+settings="$claude_home/settings.json"
+backup="$claude_home/settings.json.dotfiles-backup"
+managed="$repo_root/claude/settings.managed.json"
+
+test "$(jq -r '.attribution.commit' "$settings")" = ""
+test "$(jq -r '.attribution.pr' "$settings")" = ""
+test "$(jq -r '.attribution.sessionUrl' "$settings")" = "false"
+test "$(jq -r '.outputStyle' "$settings")" = "Concise"
+test "$(jq -r '.statusLine.type' "$settings")" = "command"
+test "$(jq -r '.statusLine.command' "$settings")" = "~/.claude/statusline.sh"
+test "$(jq -r '.statusLine.padding' "$settings")" = "0"
+test "$(jq -r '.model' "$settings")" = "keep-me"
+test "$(jq -r '.enabledPlugins.local' "$settings")" = "true"
+test "$(jq -r 'has("permissions")' "$managed")" = "false"
+test "$(jq -r 'has("hooks")' "$managed")" = "false"
+test "$(jq -r 'has("enabledPlugins")' "$managed")" = "false"
+test "$(stat -f '%Lp' "$settings")" = "600"
+test -f "$backup"
+test "$(shasum -a 256 "$backup" | awk '{print $1}')" = "$original_hash"
+
+first_hash=$(shasum -a 256 "$settings" | awk '{print $1}')
+CLAUDE_CONFIG_DIR="$claude_home" "$repo_root/claude/sync-settings.sh"
+second_hash=$(shasum -a 256 "$settings" | awk '{print $1}')
+test "$first_hash" = "$second_hash"
+test "$(shasum -a 256 "$backup" | awk '{print $1}')" = "$original_hash"
+
+invalid_hash=$(shasum -a 256 "$invalid_home/settings.json" | awk '{print $1}')
+set +e
+CLAUDE_CONFIG_DIR="$invalid_home" "$repo_root/claude/sync-settings.sh" >/dev/null 2>&1
+status=$?
+set -e
+test "$status" -ne 0
+test "$(shasum -a 256 "$invalid_home/settings.json" | awk '{print $1}')" = "$invalid_hash"
+
+echo "Claude settings sync applies portable defaults and preserves local settings"
diff --git a/tests/codex-sync-config.sh b/tests/codex-sync-config.sh
new file mode 100755
index 0000000..b0d3910
--- /dev/null
+++ b/tests/codex-sync-config.sh
@@ -0,0 +1,70 @@
+#!/usr/bin/env sh
+
+set -eu
+
+test_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+repo_root=$(CDPATH= cd -- "$test_dir/.." && pwd)
+test_root=$(mktemp -d "${TMPDIR:-/tmp}/codex-sync.XXXXXX")
+codex_home="$test_root/codex-home"
+invalid_home="$test_root/invalid-home"
+
+cleanup() {
+  rm -rf "$test_root"
+}
+trap cleanup EXIT HUP INT TERM
+
+mkdir -p "$codex_home" "$invalid_home"
+cp "$test_dir/fixtures/codex/config.toml" "$codex_home/config.toml"
+cp "$test_dir/fixtures/codex/invalid-config.toml" "$invalid_home/config.toml"
+
+original_hash=$(shasum -a 256 "$codex_home/config.toml" | awk '{print $1}')
+CODEX_HOME="$codex_home" "$repo_root/codex/sync-config.sh"
+
+config="$codex_home/config.toml"
+backup="$codex_home/config.toml.dotfiles-backup"
+
+assert_value() {
+  expression=$1
+  expected=$2
+  actual=$(yq --input-format=toml --output-format=yaml --unwrapScalar "$expression" "$config")
+  if [ "$actual" != "$expected" ]; then
+    echo "expected $expression to be $expected, got $actual" >&2
+    exit 1
+  fi
+}
+
+assert_value '.model' 'keep-me'
+assert_value '.model_verbosity' 'low'
+assert_value '.model_reasoning_summary' 'concise'
+assert_value '.personality' 'pragmatic'
+assert_value '.approvals_reviewer' 'auto_review'
+assert_value '.project_doc_fallback_filenames[0]' 'CLAUDE.md'
+assert_value '.project_doc_max_bytes' '196608'
+assert_value '.notify[0]' '/bin/sh'
+assert_value '.desktop."git-branch-prefix"' 'akan72/'
+assert_value '.desktop."git-pull-request-merge-method"' 'squash'
+assert_value '.desktop."git-commit-instructions"' 'Commit messages should be concise, just one sentence'
+assert_value '.desktop."git-pr-instructions" | contains("## Summary")' 'true'
+assert_value '.desktop."ambient-suggestions-enabled"' 'false'
+assert_value '.projects."/tmp/example".trust_level' 'trusted'
+assert_value '.mcp_servers.local.command' 'true'
+
+test "$(stat -f '%Lp' "$config")" = "600"
+test -f "$backup"
+test "$(shasum -a 256 "$backup" | awk '{print $1}')" = "$original_hash"
+
+first_hash=$(shasum -a 256 "$config" | awk '{print $1}')
+CODEX_HOME="$codex_home" "$repo_root/codex/sync-config.sh"
+second_hash=$(shasum -a 256 "$config" | awk '{print $1}')
+test "$first_hash" = "$second_hash"
+test "$(shasum -a 256 "$backup" | awk '{print $1}')" = "$original_hash"
+
+invalid_hash=$(shasum -a 256 "$invalid_home/config.toml" | awk '{print $1}')
+set +e
+CODEX_HOME="$invalid_home" "$repo_root/codex/sync-config.sh" >/dev/null 2>&1
+status=$?
+set -e
+test "$status" -ne 0
+test "$(shasum -a 256 "$invalid_home/config.toml" | awk '{print $1}')" = "$invalid_hash"
+
+echo "Codex config sync preserves local settings and applies managed values"
diff --git a/tests/fixtures/bin/brew b/tests/fixtures/bin/brew
new file mode 100755
index 0000000..3e156ec
--- /dev/null
+++ b/tests/fixtures/bin/brew
@@ -0,0 +1,3 @@
+#!/usr/bin/env sh
+
+exit 0
diff --git a/tests/fixtures/bin/codex b/tests/fixtures/bin/codex
new file mode 100755
index 0000000..bc3480a
--- /dev/null
+++ b/tests/fixtures/bin/codex
@@ -0,0 +1,4 @@
+#!/usr/bin/env sh
+
+printf '%s\n' "$*" > "$TEST_CODEX_MARKER"
+exit 1
diff --git a/tests/fixtures/claude/invalid-settings.json b/tests/fixtures/claude/invalid-settings.json
new file mode 100644
index 0000000..cbad912
--- /dev/null
+++ b/tests/fixtures/claude/invalid-settings.json
@@ -0,0 +1,3 @@
+{
+  "invalid":
+}
diff --git a/tests/fixtures/claude/settings.json b/tests/fixtures/claude/settings.json
new file mode 100644
index 0000000..ac760d4
--- /dev/null
+++ b/tests/fixtures/claude/settings.json
@@ -0,0 +1,10 @@
+{
+  "model": "keep-me",
+  "attribution": {
+    "commit": "old commit attribution",
+    "pr": "old PR attribution"
+  },
+  "enabledPlugins": {
+    "local": true
+  }
+}
diff --git a/tests/fixtures/codex/config.toml b/tests/fixtures/codex/config.toml
new file mode 100644
index 0000000..95d9847
--- /dev/null
+++ b/tests/fixtures/codex/config.toml
@@ -0,0 +1,12 @@
+model = "keep-me"
+model_verbosity = "high"
+
+[desktop]
+git-branch-prefix = "local/"
+ambient-suggestions-enabled = false
+
+[projects."/tmp/example"]
+trust_level = "trusted"
+
+[mcp_servers.local]
+command = "true"
diff --git a/tests/fixtures/codex/invalid-config.toml b/tests/fixtures/codex/invalid-config.toml
new file mode 100644
index 0000000..51cccb1
--- /dev/null
+++ b/tests/fixtures/codex/invalid-config.toml
@@ -0,0 +1 @@
+not_a_real_codex_setting = true