diff --git a/CLAUDE.md b/CLAUDE.md
index d6025e3..efafb1c 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -4,7 +4,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 ## What This Is
 
-A minimal Docker Compose setup for running LabKey Community Edition locally. Two services: `community` (LabKey app on Tomcat) and `pg-community` (PostgreSQL 17).
+A minimal Docker Compose setup for running LabKey Community Edition locally. Two services: `community` (LabKey app on Tomcat) and `pg-community` (PostgreSQL — 18 by default, override with `PG_VERSION`).
 
 ## Common Commands
 
@@ -19,7 +19,7 @@ docker compose down
 docker compose down -v --remove-orphans
 
 # Override image version at launch
-export IDENT="labkeyteamcity/labkey-community:26.3.0" && docker compose up community --detach
+COMPOSE_IMAGE="labkeyteamcity/labkey-community:26.3.0" docker compose up community --detach
 ```
 
 Access at `https://localhost:8443` after startup (self-signed cert — expect browser warning).
@@ -32,6 +32,7 @@ Key overridable variables:
 - `COMPOSE_IMAGE` — LabKey image tag (default: `labkeyteamcity/labkey-community:26.3.0`)
 - `HOST_PORT` — host HTTPS port (default: `8443`)
 - `PG_PORT` — host PostgreSQL port (default: `54321`)
+- `PG_VERSION` — PostgreSQL major version / `pg-community` image tag (default: `18`); also the data-dir suffix
 - `POSTGRES_PASSWORD` — shared between both services
 - `MAX_JVM_RAM_PERCENT` — JVM heap ceiling (default: `75.0`)
 - `LABKEY_CREATE_INITIAL_USER` / `LABKEY_CREATE_INITIAL_USER_APIKEY` — skip setup wizard if set
@@ -42,7 +43,7 @@ Key overridable variables:
 `mounts/` is gitignored. Do not delete these without understanding the consequences:
 - `mounts/files/` — LabKey file storage
 - `mounts/logs/` — server logs
-- `mounts/pgdata/` — PostgreSQL data files (subdirectory keyed by `$IDENT`)
+- `mounts/pgdata/` — PostgreSQL data files (subdirectory keyed by `$IDENT` and `$PG_VERSION`)
 - `mounts/modules/` — custom/external LabKey modules
 
 ## Upgrading LabKey Version
@@ -52,3 +53,21 @@ Edit the `image:` line in `docker-compose.yml` (or set `COMPOSE_IMAGE`). Only ta
 ## Branching and PR Workflow
 
 The `.github/workflows/workflow.yml` runs `LabKey/gitHubActions/validate-pr@develop` on all PRs. It only executes for PRs from the `LabKey` org. Feature branches follow the pattern `fb_<version>_<description>` based on recent history.
+
+## Commit and PR Body Formatting
+
+Applies to every commit body and every PR body, without exception. Do not hard-wrap. Write each paragraph and each bullet as a single physical line, no matter how long. Separate paragraphs with one blank line. This applies to text passed via `-m`, `--body`, here-docs, `gh pr edit`, GitHub MCP tools — every channel that produces commit or PR body text.
+
+**Why:** GitHub renders commit and PR bodies as GFM with hard-line-break enabled. Every mid-paragraph `\n` becomes a visible `<br>` in the rendered output, producing ragged, broken-looking text. Soft-wrap is the renderer's job, not yours.
+
+**Self-check before invoking `git commit`, `gh pr create`, or `gh pr edit`:** look at the body text you are about to pass. If any paragraph spans more than one line in your tool call, that is a bug — collapse it to a single line first. Long lines are correct. Wrapped lines are wrong.
+
+## Commit Messages
+
+Subject: short imperative (≈70 chars). Body: follow the formatting rule above — one physical line per paragraph, blank lines between paragraphs.
+
+## Pull Request Format
+
+If the repo has a `pull_request_template.md` (typically under `.github/`), follow it. Otherwise, include sections for: **Rationale** (why the change is needed), **Related Pull Requests**, and **Changes** (notable items). Keep descriptions brief. Follow the formatting rule above — one physical line per paragraph and per bullet.
+
+Before opening a PR, always draft the title and description and confirm them with the user. Do not run `gh pr create` until the user approves.
diff --git a/README.md b/README.md
index 1ff45d0..71efd2a 100644
--- a/README.md
+++ b/README.md
@@ -60,5 +60,31 @@ There are a substantial number of configuration options available.  The `docker-
 ### Upgrading versions
 We only publish tagged versions to Docker Hub (we don't publish a 'latest' tag). To upgrade to a new version of LabKey Community edition, you have two options:
 1. Edit the `docker-compose.yml` file and update the `image` version to the LabKey version you wish to use. 
-2. Launch a new version with the `docker compose up` command line.
-`export IDENT="labkeyteamcity/labkey-community:26.3.0" docker compose up community --detach`
\ No newline at end of file
+2. Launch a new version from the command line by setting `COMPOSE_IMAGE`.
+`COMPOSE_IMAGE="labkeyteamcity/labkey-community:26.3.0" docker compose up community --detach`
+
+### PostgreSQL version
+
+The database defaults to **PostgreSQL 18** (`image: postgres:${PG_VERSION:-18}`). The major
+version is included in the data-directory name (`./mounts/pgdata/<IDENT>-<PG_VERSION>-data`), so
+each version keeps its own directory on disk.
+
+PostgreSQL will not read a data directory created by an older major version, so an existing
+Postgres 17 database cannot be started by the Postgres 18 image in place:
+
+- **Start fresh on Postgres 18 (simplest):** just `docker compose up community --detach`. A new,
+  empty data directory is created; your old data under `./mounts/pgdata/postgres-data` is left
+  untouched (delete it once you no longer need it).
+- **Keep your existing Postgres 17 data:** pin the old version — `PG_VERSION=17 docker compose up
+  community --detach`. If your data predates this change it lives in the legacy
+  `./mounts/pgdata/postgres-data` directory; rename it to `postgres-17-data` first.
+
+To carry real data forward, dump from a running Postgres 17 container and restore into Postgres 18:
+
+```bash
+PG_VERSION=17 docker compose up -d pg-community
+docker compose exec pg-community pg_dumpall -U postgres > dump.sql
+PG_VERSION=17 docker compose down
+docker compose up -d pg-community          # Postgres 18, fresh data dir
+cat dump.sql | docker compose exec -T pg-community psql -U postgres
+```
\ No newline at end of file
diff --git a/docker-compose.yml b/docker-compose.yml
index cd835af..7e207b2 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -67,15 +67,22 @@ services:
       - PURGE_HEAP_AND_ERROR_LOGS_OLDER_THAN_DAYS=${PURGE_HEAP_AND_ERROR_LOGS_OLDER_THAN_DAYS:-90}
 
   pg-community:
-    image: postgres:17
+    image: postgres:${PG_VERSION:-18}
     container_name: pg-community
+    # run postgres through the image entrypoint; logs stay visible so
+    # version/startup errors (e.g. pg data-dir incompatibility) surface in
+    # `docker compose logs` instead of the container silently crash-looping.
     entrypoint:
       - "/bin/bash"
       - "-c"
-      - "docker-entrypoint.sh postgres >/dev/null 2>&1"
+      - "docker-entrypoint.sh postgres"
     environment:
       # we recommend changing this to a strong random password of at least 16 characters
       - POSTGRES_PASSWORD=${POSTGRES_PASSWORD:-a"placeholder#'password}
+      # pin PGDATA to the pre-18 default so the bind mount below keeps
+      # persisting data: the postgres:18 image moved its default PGDATA to
+      # /var/lib/postgresql/18/docker, which would bypass this mount entirely.
+      - PGDATA=/var/lib/postgresql/data
     healthcheck:
       test: ["CMD", "pg_isready", "-U", "postgres"]
       interval: 30s
@@ -83,7 +90,7 @@ services:
       retries: 3
       start_period: 40s
     volumes:
-      - ./mounts/pgdata/${IDENT:-postgres}-data:/var/lib/postgresql/data
+      - ./mounts/pgdata/${IDENT:-postgres}-${PG_VERSION:-18}-data:/var/lib/postgresql/data
     ports:
       - ${PG_PORT:-54321}:5432