Reject keep-executes-locally, switch to a .keep-vault marker file

Two changes based on further review:

- Explicitly considers and rejects letting keep's server execute the
  redeploy directly on announce, even though co-location removes the
  credential/network objection that sank the CI-SSHes-in alternative.
  The reason it's still wrong: a fully compromised keep server today
  can't do anything worse than leak ciphertext, since it never holds a
  decryption key. Giving it exec capability breaks that property — a
  routine web app bug becomes "triggers arbitrary redeploys," not
  "leaks encrypted blobs." Also notes the concrete cost: doing this
  from inside a container needs the Docker socket mounted in, which is
  broadly equivalent to root on the host.

- Replaces the "vault key = deploy directory name" assumption with an
  explicit .keep-vault marker file per project directory. Repo name,
  deploy directory name, and vault key are three independent strings
  in practice (confirmed by a real example already in this fleet) —
  no naming convention should assume any two of them match. Bootstrap
  is now: choose a vault key, keep push it, drop a one-line
  .keep-vault file. CI's announce step uses the same deliberately
  hardcoded key, never derived from the repo name automatically.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

PROPOSAL-announce-and-agent.md

@@ -98,6 +98,38 @@ happens today (a plain `docker compose up -d`, relying on that project's
 own `pull_policy: always`) for anything not yet bootstrapped, rather than
 either blocking deploys entirely or hard-failing on missing vaults.
 
+### Considered and rejected: `keep` executes the redeploy itself
+
+Since `keep`'s own server will run on the same VPS as the deploy targets,
+it's tempting to skip the polling indirection entirely and have `keep`
+shell out to the deploy script directly when it receives an `announce` —
+no new SSH credential, no new network-reachable pathway, since nothing
+is reaching *into* the box that wasn't already running on it.
+
+Rejected anyway, because it trades away a property that's been the
+throughline of `keep`'s whole design: **today, a fully compromised
+`keep` server — not just a compromised client identity — can't do
+anything worse than leak ciphertext and metadata**, because the server
+never holds a decryption key. The moment `keep` can also execute a
+command on `announce`, that stops being true — a bug in the HTTP layer
+(not even a cryptographic break; an ordinary web app bug, an auth check
+wrong on some edge case) becomes "attacker triggers arbitrary
+redeploys," not "attacker sees encrypted blobs they can't read." That's
+a new class of bad outcome, not a bigger version of an existing one, and
+it's not worth trading for skipping a polling loop.
+
+There's also a concrete operational cost, not just a principle: actually
+running `docker compose up -d` from inside `keep`'s own process would
+need either the Docker socket mounted into `keep`'s container
+(`/var/run/docker.sock` — widely treated as equivalent to handing that
+container root on the host) or running `keep` outside a container
+entirely, throwing away the isolation its own `Dockerfile` already
+provides today.
+
+`keep` stays a pure relay regardless of where it's deployed. Something
+*outside* `keep`'s own process boundary does the polling and the
+executing — see §4.
+
 ## Design
 
 ### 1. `announce` — a distinct verb from `push`/`pull`
@@ -172,17 +204,24 @@ for project in "${PROJECTS[@]}"; do
   echo ""
   echo "▶ $project"
 
-  # Best-effort: does this machine have a working keep grant for
+  # A vault key is NOT assumed to match the deploy-directory name — repo
-  # "$project/production"? If not — not bootstrapped onto keep yet, or
+  # names, deploy directory names, and vault keys are three independent
-  # never will be (a static site with no secrets) — fall through to
+  # strings in practice (a repo can be named one thing, its deploy
-  # exactly what this script already did before keep existed. Every
+  # directory another, entirely by history/accident). .keep-vault is an
-  # keep call here is allowed to fail; failure means "keep doesn't
+  # explicit, one-time-per-project marker: if it's missing, this project
-  # apply to this project," never "stop the deploy."
+  # was never bootstrapped onto keep (or never will be — a static site
-  if keep pull "$project/production" --out "$dir/.env.new" 2>/dev/null; then
+  # with no secrets), and the loop falls through to exactly what it did
+  # before keep existed. Every keep call here is allowed to fail;
+  # failure means "keep doesn't apply to this project," never "stop the
+  # deploy."
+  if [ -f "$dir/.keep-vault" ]; then
+    vault="$(cat "$dir/.keep-vault")"
+    if keep pull "$vault" --out "$dir/.env.new" 2>/dev/null; then
       mv "$dir/.env.new" "$dir/.env"
     else
       rm -f "$dir/.env.new"
     fi
+  fi
 
   if (cd "$dir" && docker compose up -d 2>&1); then
     echo "  ✓ $project up"
@@ -193,8 +232,12 @@ for project in "${PROJECTS[@]}"; do
 done
 ```
 
-Vault key convention: `<project>/production`, using the exact directory
+Bootstrapping a project onto `keep` becomes: choose a vault key (no
-name already in `PROJECTS` — no separate mapping table to keep in sync.
+naming constraint — doesn't need to match the repo or the directory),
+`keep push` it, grant whichever recipients need it, and
+`echo "<the vault key>" > "$dir/.keep-vault"`. One file, human-readable,
+`cat`-able to check what's configured, no second array in this script to
+keep in sync by hand as directories get renamed or reorganized.
 
 Notice `announce`/`watch` aren't actually load-bearing in this version —
 whatever already triggers this script (cron, systemd timer, or still
@@ -249,6 +292,17 @@ project hasn't been bootstrapped onto `keep` yet):
   run: keep announce myapp/production --tag ${{ steps.meta.outputs.short_sha }}
 ```
 
+The vault key here (`myapp/production`) is a **literal, hardcoded string
+in this specific repo's own workflow file** — never derived from
+`${{ github.repository }}` or any other automatic source. Same reasoning
+as §4's `.keep-vault` file: the repo's own name, its deploy directory's
+name, and its vault key are three independent strings that happen to
+often look similar and are not guaranteed to match (see Context — a real
+example already exists in this fleet). Whoever bootstraps a project onto
+`keep` should paste the same deliberately-chosen vault key into both this
+workflow step and that project's `.keep-vault` file, not rely on either
+side inferring it from something else.
+
 `continue-on-error: true` is load-bearing, not incidental — a project
 without a `keep` identity registered yet must still build and push its
 image successfully. This step failing should be silent/expected for any
@@ -287,6 +341,13 @@ not-yet-bootstrapped project, not a red X on the workflow.
 
 ## Open questions
 
+- **`.keep-vault` format** — a bare vault-key string is enough for
+  today's one-environment-per-directory reality. If a directory ever
+  needs to deploy more than one environment from the same
+  `docker-compose.yml` (unlikely given the current fleet shape, but not
+  impossible), a bare string stops being enough and it'd need to become
+  a small key=value file or similar. Not designing that ahead of an
+  actual need — ship the bare-string version.
 - **Fleet-wide `pull_policy: always` sweep** — a prerequisite this
   proposal depends on but doesn't itself fix (see Context). Should
   happen before or alongside this work, as its own small pass, not