Resolve open design questions: write-scoped grants, rollback, purge

Per-question resolution, per best practice rather than deferral:

- Push authorization: closed the least-privilege gap where read implied
  write. vault_grants gained can_write (default true, so nothing
  existing changes); enforced on push and grant (granting others is
  itself a mutation of vault membership, so it needs write too, not
  just read). 'keep grant --read-only' creates a read-only grant.

- Version history: not full history (conflates "undo a typo'd push"
  with "this leaked, stop retaining it" into one mechanism). Retains
  exactly one previous version as a rollback safety net
  (vaults.prev_ciphertext/prev_nonce + a vault_grants_previous mirror
  table so recipients can unwrap it), plus 'keep push --purge' for
  compromise-driven rotations that explicitly skips retention and
  wipes any existing previous version too.

- Per-secret-key granularity: resolved by NOT building it — documented
  the escape hatch (split into more vaults) instead of adding partial-
  decrypt complexity for a problem the existing primitive solves.

One more real bug caught during verification: the CLI's --previous flag
initially signed a path including its query string, but the server
verifies against req.originalUrl with the query stripped — a mismatch
that would have made every --previous request fail signature
verification. Fixed by splitting the signed path from the request URL
in signedFetch, signing only the former.

Verified end-to-end with three independent identities: read-only grant
correctly blocked from push and from granting others, write access and
read-only status both preserved correctly across a rotation, previous-
version pull working for a routine push and correctly unavailable to
every recipient after a purge push. Also re-verified against a fresh
Docker build.

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

IMPLEMENTATION.md

@@ -234,18 +234,43 @@ which would have silently mismatched a client that signs the full request
 path. Fixed by verifying against `req.originalUrl` (path portion only)
 instead, which stays consistent regardless of router nesting.
 
-## Open questions
+## Resolved design decisions
 
-- **Version history**: keep only the latest payload per vault (what got
+These were open questions at initial implementation; resolved as follows.
-  built), or retain N previous versions for `keep pull --version=N`
+
-  rollback? Skipped for v1, revisit if a real rollback need shows up.
+### Version history: one previous version, not full history
-- **Push authorization**: does having a *read* grant (`vault_grants` row)
+
-  imply push rights too, or is push a separate capability? Went with
+Full N-version history (what Vault/AWS Secrets Manager do) conflates two
-  "read implies write" for v1 — a `can_write` flag on `vault_grants` is
+different needs that deserve different treatment: "I pushed a typo'd
-  the natural extension if that turns out to be wrong.
+value, let me roll back" wants a safety net; "this credential leaked"
-- **Per-secret-key granularity**: v1 treats a vault as one opaque
+wants the old value to stop existing anywhere retrievable, which a kept
-  `.env`-shaped blob (matches the actual pain point this was built for:
+version directly undermines. Resolution: retain exactly the immediately
-  whole files get copied around, not individual keys). If a use case
+previous payload as a rollback safety net (`keep pull --previous`), plus
-  emerges for "grant access to just one value, not the whole bundle,"
+an explicit hard-rotate mode (`keep push --purge`) that skips retention
-  that's a genuinely different data model (per-key rows, each separately
+entirely for compromise-driven rotations. Not full history — the two
-  wrapped) — don't half-build it speculatively.
+real use cases are served without the complexity (or the confused
+security story) of an unbounded log of past secret values.
+
+### Push authorization: read no longer implies write
+
+The original "read implies write" v1 simplification was a real
+least-privilege gap: an automated deploy identity that only ever needs
+to *pull* a vault also had the power to overwrite it — a compromised
+read-only consumer could push garbage values or silently exclude other
+recipients from the next rotation. Fixed rather than deferred, since the
+cost of closing it is low and the cost of retrofitting it later (once
+grants without write intent already exist) is higher: `vault_grants`
+gained a `can_write` column (`1` by default, so nothing existing
+changes behavior), enforced in the push handler, with `keep grant
+--read-only` to create a read-only grant explicitly.
+
+### Per-secret-key granularity: resolved by not building it
+
+The right answer for "different recipients need different subsets of
+secrets" is splitting into more vaults (`myapp/db`, `myapp/api`, each
+with their own recipient list), not partial-access ACLs within one
+blob. A vault staying the permission boundary keeps the mental model
+simple and auditable; per-key wrapping would solve the same problem
+with materially more complexity for no real gain over just making more
+vaults. No code change — this documents the escape hatch instead of
+leaving a dangling TODO.

README.md

@@ -102,20 +102,34 @@ npm run cli -- pull myapp/production > .env
 
 ```bash
 # An existing recipient of a vault can grant a NEW recipient access,
-# without needing admin rights or re-encrypting the payload:
+# without needing admin rights or re-encrypting the payload. Read access
+# by default — add --read-only for a recipient that should only ever
+# pull, never push (e.g. an automated deploy identity):
 keep grant myapp/production <new-recipient-id>
+keep grant myapp/production <deploy-recipient-id> --read-only
 
 # Revoking is an admin operation — pure metadata deletion, immediate:
 KEEP_ADMIN_PASSWORD=... keep revoke myapp/production <recipient-id>
 
 # Revoke only stops FUTURE pulls. If this was a compromise response,
-# also rotate the actual values:
+# rotate AND purge — --purge skips retaining the outgoing version as a
+# rollback, since the whole point of rotating for a leak is that the old
+# value stops being retrievable by anyone:
+keep push myapp/production --file .env.production --purge
+
+# A routine push (no compromise involved) keeps the outgoing version as
+# a one-step rollback safety net:
 keep push myapp/production --file .env.production
+keep pull myapp/production --previous   # "oops, undo that last push"
 
 # See who's touched a vault and when:
 keep log myapp/production
 ```
 
+Pushing to an existing vault requires a *write* grant — a read-only
+recipient can pull but can't push or grant others access. A brand-new
+vault's first push is always read-write for the pusher.
+
 ## Docker
 
 ```bash
@@ -150,13 +164,17 @@ CLI-side: `KEEP_SERVER_URL` (default `http://localhost:3050`),
 
 ## Status
 
-Implemented: identity, push/pull/grant/revoke/log, admin recipient
+Implemented: identity, push/pull/grant/revoke/log, read/write grant
-management, Docker deploy. Verified end-to-end (two independent
+scoping, one-step rollback with an explicit purge mode for
-identities, grant, pull, revoke persisting through a subsequent
+compromise-driven rotations, admin recipient management, Docker deploy.
-rotation, malformed-auth rejection) against both a local server and the
+Verified end-to-end — two and three independent identities, read-only
-built Docker image. See [IMPLEMENTATION.md](./IMPLEMENTATION.md) for the
+grants correctly blocked from push/grant, grants preserved across
-full design and its still-open questions (version history, per-secret-key
+rotation, previous-version pull working and correctly wiped by
-granularity).
+`--purge` for every recipient, malformed-auth rejection — against both
+a local server and the built Docker image. See
+[IMPLEMENTATION.md](./IMPLEMENTATION.md) for the full design and its
+resolved decisions (per-secret-key granularity deliberately not built —
+use multiple vaults instead).
 
 ## License
 

src/cli/commands/vault.ts

@@ -11,7 +11,7 @@ import {
   enc,
 } from '../../shared/crypto.js';
 
-export async function vaultPush(vaultKey: string, file: string): Promise<void> {
+export async function vaultPush(vaultKey: string, file: string, purge: boolean): Promise<void> {
   await ready();
   const { identity, recipientId } = await requireIdentityAndRecipientId();
 
@@ -21,8 +21,11 @@ export async function vaultPush(vaultKey: string, file: string): Promise<void> {
 
   const existsRes = await expectOk(await signedFetch(identity, recipientId, 'GET', `/api/vaults/${encodeURIComponent(vaultKey)}/exists`));
 
-  const wrapFor = new Map<string, string>(); // recipientId -> publicKey
+  // recipientId -> { publicKey, canWrite } — canWrite is preserved across
-  wrapFor.set(recipientId, identity.id);
+  // a rotation, not reset, so pushing an update never silently changes
+  // who else can write vs. only read.
+  const wrapFor = new Map<string, { publicKey: string; canWrite: boolean }>();
+  wrapFor.set(recipientId, { publicKey: identity.id, canWrite: true });
 
   if (existsRes.exists) {
     const recipientsRes = await signedFetch(identity, recipientId, 'GET', `/api/vaults/${encodeURIComponent(vaultKey)}/recipients`);
@@ -30,32 +33,34 @@ export async function vaultPush(vaultKey: string, file: string): Promise<void> {
       const body = await recipientsRes.json().catch(() => ({}));
       throw new Error(body.error ?? `no access to vault '${vaultKey}' — ask an existing grantee to run 'keep grant ${vaultKey} ${recipientId}'`);
     }
-    const current = await recipientsRes.json() as { recipientId: string; publicKey: string }[];
+    const current = await recipientsRes.json() as { recipientId: string; publicKey: string; canWrite: boolean }[];
-    for (const r of current) if (r.publicKey) wrapFor.set(r.recipientId, r.publicKey);
+    for (const r of current) if (r.publicKey) wrapFor.set(r.recipientId, { publicKey: r.publicKey, canWrite: r.canWrite });
   }
 
   const symmetricKey = generateSymmetricKey();
   const { nonce, ciphertext } = secretboxEncrypt(symmetricKey, payload);
 
-  const wrappedKeys: Record<string, string> = {};
+  const wrappedKeys: Record<string, { wrappedKey: string; canWrite: boolean }> = {};
-  for (const [rid, pubHex] of wrapFor) {
+  for (const [rid, { publicKey, canWrite }] of wrapFor) {
-    wrappedKeys[rid] = enc.toBase64(Identity.sealFor(pubHex, symmetricKey));
+    wrappedKeys[rid] = { wrappedKey: enc.toBase64(Identity.sealFor(publicKey, symmetricKey)), canWrite };
   }
 
   await expectOk(await signedFetch(identity, recipientId, 'POST', `/api/vaults/${encodeURIComponent(vaultKey)}/push`, {
     ciphertext: enc.toBase64(ciphertext),
     nonce: enc.toBase64(nonce),
     wrappedKeys,
+    purge,
   }));
 
-  console.log(`pushed '${vaultKey}' — ${Object.keys(values).length} key${Object.keys(values).length === 1 ? '' : 's'}, wrapped for ${wrapFor.size} recipient${wrapFor.size === 1 ? '' : 's'}.`);
+  console.log(`pushed '${vaultKey}' — ${Object.keys(values).length} key${Object.keys(values).length === 1 ? '' : 's'}, wrapped for ${wrapFor.size} recipient${wrapFor.size === 1 ? '' : 's'}${purge ? ' (purged previous version)' : ''}.`);
 }
 
-export async function vaultPull(vaultKey: string, format: 'env' | 'json', outFile?: string): Promise<void> {
+export async function vaultPull(vaultKey: string, format: 'env' | 'json', outFile: string | undefined, previous: boolean): Promise<void> {
   await ready();
   const { identity, recipientId } = await requireIdentityAndRecipientId();
 
-  const data = await expectOk(await signedFetch(identity, recipientId, 'GET', `/api/vaults/${encodeURIComponent(vaultKey)}/pull`));
+  const query = previous ? '?previous=1' : '';
+  const data = await expectOk(await signedFetch(identity, recipientId, 'GET', `/api/vaults/${encodeURIComponent(vaultKey)}/pull${query}`));
 
   const symmetricKey = identity.openSealed(enc.fromBase64(data.wrappedKey));
   if (!symmetricKey) throw new Error('failed to unwrap this vault\'s key — wrong identity, or the grant is stale');
@@ -66,13 +71,13 @@ export async function vaultPull(vaultKey: string, format: 'env' | 'json', outFil
   const out = format === 'json' ? JSON.stringify(values, null, 2) : serializeEnv(values);
   if (outFile) {
     fs.writeFileSync(outFile, out);
-    console.error(`wrote ${Object.keys(values).length} key(s) to ${outFile}`);
+    console.error(`wrote ${Object.keys(values).length} key(s) to ${outFile}${previous ? ' (previous version)' : ''}`);
   } else {
     process.stdout.write(out);
   }
 }
 
-export async function vaultGrant(vaultKey: string, targetRecipientId: string): Promise<void> {
+export async function vaultGrant(vaultKey: string, targetRecipientId: string, readOnly: boolean): Promise<void> {
   await ready();
   const { identity, recipientId } = await requireIdentityAndRecipientId();
 
@@ -88,15 +93,16 @@ export async function vaultGrant(vaultKey: string, targetRecipientId: string): P
   await expectOk(await signedFetch(identity, recipientId, 'POST', `/api/vaults/${encodeURIComponent(vaultKey)}/grant`, {
     recipientId: targetRecipientId,
     wrappedKey,
+    canWrite: !readOnly,
   }));
 
-  console.log(`granted '${vaultKey}' to ${targetRecipientId}.`);
+  console.log(`granted ${readOnly ? 'read-only ' : ''}'${vaultKey}' access to ${targetRecipientId}.`);
 }
 
 export async function vaultRevoke(vaultKey: string, targetRecipientId: string): Promise<void> {
   await expectOk(await adminFetch('DELETE', `/api/admin/vaults/${encodeURIComponent(vaultKey)}/grants/${encodeURIComponent(targetRecipientId)}`));
   console.log(`revoked ${targetRecipientId}'s access to '${vaultKey}'.`);
-  console.log(`Note: this stops future pulls only. If this was a compromise response, also run 'keep push ${vaultKey}' with rotated values.`);
+  console.log(`Note: this stops future pulls only. If this was a compromise response, also run 'keep push ${vaultKey} --purge' with rotated values.`);
 }
 
 export async function vaultLog(vaultKey: string): Promise<void> {

src/cli/index.ts

@@ -8,6 +8,10 @@ function flag(args: string[], name: string, fallback?: string): string | undefin
   return i !== -1 ? args[i + 1] : fallback;
 }
 
+function boolFlag(args: string[], name: string): boolean {
+  return args.includes(`--${name}`);
+}
+
 async function main(): Promise<void> {
   const [, , cmd, sub, ...rest] = process.argv;
 
@@ -24,9 +28,9 @@ async function main(): Promise<void> {
       if (sub === 'remove') return await recipientRemove(rest[0]);
     }
 
-    if (cmd === 'push') return await vaultPush(sub, flag(rest, 'file', '.env')!);
+    if (cmd === 'push') return await vaultPush(sub, flag(rest, 'file', '.env')!, boolFlag(rest, 'purge'));
-    if (cmd === 'pull') return await vaultPull(sub, (flag(rest, 'format', 'env') as 'env' | 'json'), flag(rest, 'out'));
+    if (cmd === 'pull') return await vaultPull(sub, (flag(rest, 'format', 'env') as 'env' | 'json'), flag(rest, 'out'), boolFlag(rest, 'previous'));
-    if (cmd === 'grant') return await vaultGrant(sub, rest[0]);
+    if (cmd === 'grant') return await vaultGrant(sub, rest[0], boolFlag(rest, 'read-only'));
     if (cmd === 'revoke') return await vaultRevoke(sub, rest[0]);
     if (cmd === 'log') return await vaultLog(sub);
 
@@ -45,9 +49,9 @@ function printUsage(): void {
   keep identity show
   keep identity set-id <recipient-id>
 
-  keep push <vault> [--file .env]
+  keep push <vault> [--file .env] [--purge]   (--purge: don't retain the outgoing version as rollback)
-  keep pull <vault> [--format env|json] [--out <path>]
+  keep pull <vault> [--format env|json] [--out <path>] [--previous]
-  keep grant <vault> <recipient-id>
+  keep grant <vault> <recipient-id> [--read-only]
   keep revoke <vault> <recipient-id>          (admin — needs KEEP_ADMIN_PASSWORD)
   keep log <vault>
 

src/cli/signedFetch.ts

@@ -4,6 +4,16 @@ export function serverUrl(): string {
   return process.env.KEEP_SERVER_URL ?? 'http://localhost:3050';
 }
 
+function splitQuery(path: string): [string, string] {
+  const i = path.indexOf('?');
+  return i === -1 ? [path, ''] : [path.slice(0, i), path.slice(i)];
+}
+
+// `path` must NOT include a query string — the server verifies the
+// signature against req.originalUrl with the query string stripped
+// (see server/auth.ts), so signing one here would never match. Pass
+// query params via `path` only for the actual request URL, kept
+// separate from what gets signed.
 export async function signedFetch(
   identity: Identity,
   recipientId: string,
@@ -11,12 +21,13 @@ export async function signedFetch(
   path: string,
   body?: unknown,
 ): Promise<Response> {
+  const [signedPath, query] = splitQuery(path);
   const bodyBytes = body !== undefined ? enc.fromUtf8(JSON.stringify(body)) : new Uint8Array();
   const timestamp = Math.floor(Date.now() / 1000);
-  const toSign = signingString(method, path, timestamp, bodyBytes);
+  const toSign = signingString(method, signedPath, timestamp, bodyBytes);
   const signature = enc.toHex(identity.sign(enc.fromUtf8(toSign)));
 
-  return fetch(`${serverUrl()}${path}`, {
+  return fetch(`${serverUrl()}${signedPath}${query}`, {
     method,
     headers: {
       'Content-Type': 'application/json',

src/server/db.ts

@@ -13,6 +13,11 @@ db.exec(`
     vault_key       TEXT PRIMARY KEY,
     ciphertext      BLOB NOT NULL,
     nonce           BLOB NOT NULL,
+    -- Exactly one previous version, retained as a rollback safety net for
+    -- an accidental bad push — not a full history. NULL if there is no
+    -- previous version, or if the last push explicitly purged it.
+    prev_ciphertext BLOB,
+    prev_nonce      BLOB,
     updated_at      INTEGER NOT NULL,
     updated_by      TEXT NOT NULL
   );
@@ -29,10 +34,26 @@ db.exec(`
     vault_key    TEXT NOT NULL,
     recipient_id TEXT NOT NULL,
     wrapped_key  TEXT NOT NULL,  -- base64 crypto_box_seal(vault_symmetric_key, recipient_pubkey)
+    -- Read implied write in the original design; resolved to a real
+    -- capability distinction — a recipient that only needs to pull a
+    -- vault (e.g. an automated deploy identity) shouldn't also be able
+    -- to overwrite it. Defaults to 1 so nothing existing changes.
+    can_write    INTEGER NOT NULL DEFAULT 1,
     granted_at   INTEGER NOT NULL,
     PRIMARY KEY (vault_key, recipient_id)
   );
 
+  -- Mirrors vault_grants, but for the one retained previous version —
+  -- wrapped keys as they were at push time, so a recipient who had
+  -- access to the previous version can still unwrap it via --previous
+  -- even if their current grant has since changed.
+  CREATE TABLE IF NOT EXISTS vault_grants_previous (
+    vault_key    TEXT NOT NULL,
+    recipient_id TEXT NOT NULL,
+    wrapped_key  TEXT NOT NULL,
+    PRIMARY KEY (vault_key, recipient_id)
+  );
+
   CREATE TABLE IF NOT EXISTS access_log (
     id           INTEGER PRIMARY KEY AUTOINCREMENT,
     vault_key    TEXT NOT NULL,
@@ -46,6 +67,8 @@ export interface VaultRow {
   vault_key: string;
   ciphertext: Buffer;
   nonce: Buffer;
+  prev_ciphertext: Buffer | null;
+  prev_nonce: Buffer | null;
   updated_at: number;
   updated_by: string;
 }
@@ -61,6 +84,7 @@ export interface GrantRow {
   vault_key: string;
   recipient_id: string;
   wrapped_key: string;
+  can_write: number;
   granted_at: number;
 }
 
@@ -68,14 +92,71 @@ export function getVault(vaultKey: string): VaultRow | undefined {
   return db.prepare(`SELECT * FROM vaults WHERE vault_key = ?`).get(vaultKey) as VaultRow | undefined;
 }
 
-export function upsertVault(vaultKey: string, ciphertext: Buffer, nonce: Buffer, updatedBy: string): void {
+// `purge`: skip retaining the outgoing version as "previous" — used for
+// compromise-driven rotations, where the whole point is that the old
+// value stops being retrievable by anyone. A purge also clears out
+// whatever previous version already existed, since it would defeat the
+// purpose to still leave the version-before-that recoverable.
+export function pushVault(
+  vaultKey: string,
+  ciphertext: Buffer,
+  nonce: Buffer,
+  updatedBy: string,
+  wrappedByRecipientId: Map<string, { wrappedKey: string; canWrite: boolean }>,
+  purge: boolean,
+): void {
+  const tx = db.transaction(() => {
+    const existing = getVault(vaultKey);
+    const now = Math.floor(Date.now() / 1000);
+
+    if (purge) {
       db.prepare(
-    `INSERT INTO vaults (vault_key, ciphertext, nonce, updated_at, updated_by)
+        `INSERT INTO vaults (vault_key, ciphertext, nonce, prev_ciphertext, prev_nonce, updated_at, updated_by)
-     VALUES (?, ?, ?, ?, ?)
+         VALUES (?, ?, ?, NULL, NULL, ?, ?)
          ON CONFLICT(vault_key) DO UPDATE SET
            ciphertext = excluded.ciphertext, nonce = excluded.nonce,
+           prev_ciphertext = NULL, prev_nonce = NULL,
            updated_at = excluded.updated_at, updated_by = excluded.updated_by`,
-  ).run(vaultKey, ciphertext, nonce, Math.floor(Date.now() / 1000), updatedBy);
+      ).run(vaultKey, ciphertext, nonce, now, updatedBy);
+      db.prepare(`DELETE FROM vault_grants_previous WHERE vault_key = ?`).run(vaultKey);
+    } else {
+      db.prepare(
+        `INSERT INTO vaults (vault_key, ciphertext, nonce, prev_ciphertext, prev_nonce, updated_at, updated_by)
+         VALUES (?, ?, ?, ?, ?, ?, ?)
+         ON CONFLICT(vault_key) DO UPDATE SET
+           ciphertext = excluded.ciphertext, nonce = excluded.nonce,
+           prev_ciphertext = excluded.prev_ciphertext, prev_nonce = excluded.prev_nonce,
+           updated_at = excluded.updated_at, updated_by = excluded.updated_by`,
+      ).run(vaultKey, ciphertext, nonce, existing?.ciphertext ?? null, existing?.nonce ?? null, now, updatedBy);
+
+      // Move the current grants (as they stood before this push) into
+      // vault_grants_previous, so someone who had access to the
+      // outgoing version can still pull it via --previous.
+      db.prepare(`DELETE FROM vault_grants_previous WHERE vault_key = ?`).run(vaultKey);
+      if (existing) {
+        db.prepare(
+          `INSERT INTO vault_grants_previous (vault_key, recipient_id, wrapped_key)
+           SELECT vault_key, recipient_id, wrapped_key FROM vault_grants WHERE vault_key = ?`,
+        ).run(vaultKey);
+      }
+    }
+
+    db.prepare(`DELETE FROM vault_grants WHERE vault_key = ?`).run(vaultKey);
+    const insert = db.prepare(
+      `INSERT INTO vault_grants (vault_key, recipient_id, wrapped_key, can_write, granted_at) VALUES (?, ?, ?, ?, ?)`,
+    );
+    for (const [recipientId, { wrappedKey, canWrite }] of wrappedByRecipientId) {
+      insert.run(vaultKey, recipientId, wrappedKey, canWrite ? 1 : 0, now);
+    }
+  });
+  tx();
+}
+
+export function getVaultGrantsPrevious(vaultKey: string, recipientId: string): string | undefined {
+  const row = db.prepare(
+    `SELECT wrapped_key FROM vault_grants_previous WHERE vault_key = ? AND recipient_id = ?`,
+  ).get(vaultKey, recipientId) as { wrapped_key: string } | undefined;
+  return row?.wrapped_key;
 }
 
 export function getRecipient(recipientId: string): RecipientRow | undefined {
@@ -96,6 +177,7 @@ export function deleteRecipient(recipientId: string): void {
   const tx = db.transaction(() => {
     db.prepare(`DELETE FROM recipients WHERE recipient_id = ?`).run(recipientId);
     db.prepare(`DELETE FROM vault_grants WHERE recipient_id = ?`).run(recipientId);
+    db.prepare(`DELETE FROM vault_grants_previous WHERE recipient_id = ?`).run(recipientId);
   });
   tx();
 }
@@ -107,6 +189,13 @@ export function hasGrant(vaultKey: string, recipientId: string): boolean {
   return row != null;
 }
 
+export function hasWriteGrant(vaultKey: string, recipientId: string): boolean {
+  const row = db.prepare(
+    `SELECT can_write FROM vault_grants WHERE vault_key = ? AND recipient_id = ?`,
+  ).get(vaultKey, recipientId) as { can_write: number } | undefined;
+  return row != null && row.can_write === 1;
+}
+
 export function getGrant(vaultKey: string, recipientId: string): GrantRow | undefined {
   return db.prepare(
     `SELECT * FROM vault_grants WHERE vault_key = ? AND recipient_id = ?`,
@@ -117,29 +206,13 @@ export function listGrantsForVault(vaultKey: string): GrantRow[] {
   return db.prepare(`SELECT * FROM vault_grants WHERE vault_key = ?`).all(vaultKey) as GrantRow[];
 }
 
-export function setGrant(vaultKey: string, recipientId: string, wrappedKeyB64: string): void {
+export function setGrant(vaultKey: string, recipientId: string, wrappedKeyB64: string, canWrite: boolean): void {
   db.prepare(
-    `INSERT INTO vault_grants (vault_key, recipient_id, wrapped_key, granted_at)
+    `INSERT INTO vault_grants (vault_key, recipient_id, wrapped_key, can_write, granted_at)
-     VALUES (?, ?, ?, ?)
+     VALUES (?, ?, ?, ?, ?)
-     ON CONFLICT(vault_key, recipient_id) DO UPDATE SET wrapped_key = excluded.wrapped_key, granted_at = excluded.granted_at`,
+     ON CONFLICT(vault_key, recipient_id) DO UPDATE SET
-  ).run(vaultKey, recipientId, wrappedKeyB64, Math.floor(Date.now() / 1000));
+       wrapped_key = excluded.wrapped_key, can_write = excluded.can_write, granted_at = excluded.granted_at`,
-}
+  ).run(vaultKey, recipientId, wrappedKeyB64, canWrite ? 1 : 0, Math.floor(Date.now() / 1000));
-
-// Used by `push` (rotation): replaces every wrapped-key row for a vault
-// in one transaction, so a concurrent grant/revoke can't interleave with
-// a partial rewrap and leave the vault in a mixed old/new-key state.
-export function replaceAllGrantsForVault(vaultKey: string, wrappedByRecipientId: Map<string, string>): void {
-  const tx = db.transaction(() => {
-    db.prepare(`DELETE FROM vault_grants WHERE vault_key = ?`).run(vaultKey);
-    const insert = db.prepare(
-      `INSERT INTO vault_grants (vault_key, recipient_id, wrapped_key, granted_at) VALUES (?, ?, ?, ?)`,
-    );
-    const now = Math.floor(Date.now() / 1000);
-    for (const [recipientId, wrappedKeyB64] of wrappedByRecipientId) {
-      insert.run(vaultKey, recipientId, wrappedKeyB64, now);
-    }
-  });
-  tx();
 }
 
 export function deleteGrant(vaultKey: string, recipientId: string): void {

src/server/routes.ts

@@ -1,12 +1,13 @@
 import { Router } from 'express';
 import {
   getVault,
-  upsertVault,
+  pushVault,
   hasGrant,
+  hasWriteGrant,
   getGrant,
+  getVaultGrantsPrevious,
   listGrantsForVault,
   setGrant,
-  replaceAllGrantsForVault,
   logAccess,
   getAccessLog,
   listRecipients,
@@ -33,7 +34,10 @@ router.get('/vaults/:key/exists', (req, res) => {
 });
 
 // Only current grantees of a vault can see who else has access to it —
-// needed by `keep push` to know who to re-wrap the rotated key for.
+// needed by `keep push` to know who to re-wrap the rotated key for, and
+// to preserve each recipient's can_write flag across a rotation (a push
+// shouldn't silently upgrade a read-only grantee to read-write, or vice
+// versa).
 router.get('/vaults/:key/recipients', (req: AuthedRequest, res) => {
   const vaultKey = req.params.key;
   if (!hasGrant(vaultKey, req.recipientId!)) {
@@ -44,13 +48,34 @@ router.get('/vaults/:key/recipients', (req: AuthedRequest, res) => {
   const byId = new Map(listRecipients().map(r => [r.recipient_id, r]));
   res.json(grants.map(g => {
     const r = byId.get(g.recipient_id);
-    return { recipientId: g.recipient_id, label: r?.label ?? null, publicKey: r?.public_key ?? null };
+    return { recipientId: g.recipient_id, label: r?.label ?? null, publicKey: r?.public_key ?? null, canWrite: g.can_write === 1 };
   }));
 });
 
 router.get('/vaults/:key/pull', (req: AuthedRequest, res) => {
   const vaultKey = req.params.key;
   const recipientId = req.recipientId!;
+  const wantPrevious = req.query.previous === '1' || req.query.previous === 'true';
+
+  if (wantPrevious) {
+    const vault = getVault(vaultKey);
+    const wrappedKey = getVaultGrantsPrevious(vaultKey, recipientId);
+    if (!vault || !vault.prev_ciphertext || !vault.prev_nonce || !wrappedKey) {
+      logAccess(vaultKey, recipientId, 'pull');
+      res.status(404).json({ error: 'no previous version, or no access to it' });
+      return;
+    }
+    logAccess(vaultKey, recipientId, 'pull');
+    res.json({
+      ciphertext: vault.prev_ciphertext.toString('base64'),
+      nonce: vault.prev_nonce.toString('base64'),
+      wrappedKey,
+      updatedAt: null,
+      updatedBy: null,
+    });
+    return;
+  }
+
   const grant = getGrant(vaultKey, recipientId);
   const vault = getVault(vaultKey);
 
@@ -74,53 +99,74 @@ router.get('/vaults/:key/pull', (req: AuthedRequest, res) => {
 // key in one call — the client has already generated a fresh symmetric
 // key and re-wrapped it for every currently-granted recipient (fetched
 // via GET /vaults/:key/recipients first). Existing vaults require the
-// pusher to already be a grantee (read implies write, v1 decision from
+// pusher to hold a *write* grant — read no longer implies write (see
-// IMPLEMENTATION.md); a brand-new vault key may be created by any
+// IMPLEMENTATION.md's resolved design decisions). A brand-new vault key
-// registered recipient, who becomes its first grantee.
+// may be created by any registered recipient, who becomes its first
+// (read-write) grantee.
+//
+// `purge: true` skips retaining the outgoing version as "previous" —
+// for compromise-driven rotations, where the old value should stop
+// being retrievable by anyone, not survive one more pull as a rollback.
 router.post('/vaults/:key/push', (req: AuthedRequest, res) => {
   const vaultKey = req.params.key;
   const recipientId = req.recipientId!;
   const existing = getVault(vaultKey);
 
-  if (existing && !hasGrant(vaultKey, recipientId)) {
+  if (existing && !hasWriteGrant(vaultKey, recipientId)) {
-    res.status(403).json({ error: 'no access to this vault' });
+    res.status(403).json({ error: 'no write access to this vault' });
     return;
   }
 
-  const body = req.body as { ciphertext?: string; nonce?: string; wrappedKeys?: Record<string, string> };
+  const body = req.body as {
+    ciphertext?: string;
+    nonce?: string;
+    wrappedKeys?: Record<string, { wrappedKey: string; canWrite?: boolean }>;
+    purge?: boolean;
+  };
   if (!body.ciphertext || !body.nonce || !body.wrappedKeys || Object.keys(body.wrappedKeys).length === 0) {
     res.status(400).json({ error: 'ciphertext, nonce, and at least one wrapped key are required' });
     return;
   }
 
-  upsertVault(vaultKey, Buffer.from(body.ciphertext, 'base64'), Buffer.from(body.nonce, 'base64'), recipientId);
+  const wrappedByRecipientId = new Map(
-  replaceAllGrantsForVault(vaultKey, new Map(Object.entries(body.wrappedKeys)));
+    Object.entries(body.wrappedKeys).map(([rid, w]) => [rid, { wrappedKey: w.wrappedKey, canWrite: w.canWrite !== false }]),
+  );
+
+  pushVault(
+    vaultKey,
+    Buffer.from(body.ciphertext, 'base64'),
+    Buffer.from(body.nonce, 'base64'),
+    recipientId,
+    wrappedByRecipientId,
+    body.purge === true,
+  );
 
   logAccess(vaultKey, recipientId, 'push');
   res.json({ ok: true });
 });
 
 // Adds ONE new recipient to an existing vault using the CURRENT
-// (unrotated) symmetric key — the granter must already hold a grant
+// (unrotated) symmetric key — the granter must already hold a *write*
-// (meaning they can unwrap the current key locally) and supplies a fresh
+// grant (granting is a mutation of the vault's membership, not merely a
-// seal of that same key for the new recipient's public key. Does not
+// read) and supplies a fresh seal of that same key for the new
-// touch the ciphertext or any other recipient's wrapped key.
+// recipient's public key. Does not touch the ciphertext or any other
+// recipient's wrapped key.
 router.post('/vaults/:key/grant', (req: AuthedRequest, res) => {
   const vaultKey = req.params.key;
   const granterId = req.recipientId!;
 
-  if (!hasGrant(vaultKey, granterId)) {
+  if (!hasWriteGrant(vaultKey, granterId)) {
-    res.status(403).json({ error: 'no access to this vault' });
+    res.status(403).json({ error: 'no write access to this vault' });
     return;
   }
 
-  const body = req.body as { recipientId?: string; wrappedKey?: string };
+  const body = req.body as { recipientId?: string; wrappedKey?: string; canWrite?: boolean };
   if (!body.recipientId || !body.wrappedKey) {
     res.status(400).json({ error: 'recipientId and wrappedKey are required' });
     return;
   }
 
-  setGrant(vaultKey, body.recipientId, body.wrappedKey);
+  setGrant(vaultKey, body.recipientId, body.wrappedKey, body.canWrite !== false);
   logAccess(vaultKey, granterId, 'grant');
   res.json({ ok: true });
 });