Implement experimental file-based encrypted private chat

Add fixed-suite Rust/WASI identity files, signed challenge authentication, ciphertext-only SQLite storage, a minimal LibreJS-compatible interface, and consistent backup snapshots. Keep production unchanged and document the local workflow, limits, source distribution, and browser recovery tests.

1 files changed, 27 insertions, 29 deletions

diff --git a/crates/chat-crypto/README.txt b/crates/chat-crypto/README.txt
index d09ff82..e04246c 100644
--- a/crates/chat-crypto/README.txt
+++ b/crates/chat-crypto/README.txt
@@ -14,26 +14,33 @@ You should have received a copy of the GNU Affero General Public License
 along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 
-CHAT CRYPTOGRAPHY COMPATIBILITY PROBE
-
-    Experimental, local-only work on feature/private-chat. This is a
-    cryptographic compatibility test, not a messaging application. Do not use
-    it for private conversations or real identities. It creates temporary
-    identities in memory and discards them; it does not create user chat files.
+PRIVATE CHAT CRYPTOGRAPHY
 
     Fixed encryption: RFC 9980 ML-KEM-1024 + X448, OpenPGP v6.
-    Tested signing: ML-DSA-87 + Ed448, OpenPGP v6.
+    Signing: ML-DSA-87 + Ed448, OpenPGP v6.
     Backend: Sequoia 2.4.2 with OpenSSL 3.6.5. No algorithm substitution or
-    vulnerability-advisory exception was used. The first checkpoint's Rust
-    backend is historical and no longer selected.
+    vulnerability-advisory exception was used. The original RustCrypto backend
+    is historical and no longer selected.
+
+    This crate implements purpose-specific identity creation, Argon2id/AES-256-GCM
+    protected files, detached authentication proofs, signed two-recipient messages,
+    bounded verified history batches, and the original compatibility probe.
+    Native Rust and browser WASI share the implementation. The standalone command
+    accepts one JSON request on stdin; empty input runs the compatibility probe.
+    Its browser WASI host grants no filesystem or network access. Private request
+    data must remain in local memory and must never be submitted to the server.
+
+    See ../../docs/CHAT-APPLICATION.txt for implemented formats, local setup,
+    tests, backups, and limitations. Work remains experimental and local on
+    feature/private-chat. Production remains unchanged. Do not mistake the
+    compatibility probe for an application security audit.
 
-    See ../../docs/CHAT-OPENSSL-MIGRATION.txt for the complete decision record,
-    pinned source hashes, build flags, capability boundaries, dependency-policy
-    exceptions, observed results, limitations, and reproduction commands.
-    ../../docs/CHAT-SECURITY-REVIEW.txt records the original dependency findings.
-    ../../docs/CHAT-DESIGN.txt describes the planned application.
+    ../../docs/CHAT-OPENSSL-MIGRATION.txt records the complete backend decision,
+    pinned source hashes, build flags, FFI/capability limitations, and reviewed
+    dependency-policy exceptions. ../../docs/CHAT-SECURITY-REVIEW.txt records
+    the superseded RustCrypto findings without advisory ignores.
 
-QUICK CHECKS FROM THE STACK ROOT
+CHECKS FROM THE WORKSPACE ROOT
 
         cargo test --locked -p stack-chat-crypto
         cargo run --locked -p stack-chat-crypto
@@ -41,17 +48,8 @@ QUICK CHECKS FROM THE STACK ROOT
         PLAYWRIGHT_BROWSERS_PATH="$PWD/.tools/browsers" node crates/chat-crypto/tests/browser.mjs
         cargo stack check
 
-    Native checks require OpenSSL >=3.5 development files and libclang.
-    The cross-build script currently supports Linux x86_64 development hosts.
-    Browser tooling installation is documented in the migration record.
-
-    The harness serves only a blank document, a readable AGPL JavaScript WASI
-    bridge, and the new WASI binary on an ephemeral loopback port. It verifies
-    the actual OpenSSL backend, cryptographic round trips, tampering and invalid
-    credential rejection, repeated fresh instances, and failure without CSPRNG.
-    It checks for external requests and persistent browser application state.
-
-    The application itself, private chat-file envelope, and session workflow
-    remain unimplemented. LibreJS acceptance has not been tested; there is no
-    public chat page or compliance badge. The fixture password is public test
-    data, not a configured secret. No .env file or user private key is needed.
+    Native builds require OpenSSL >=3.5 development files and libclang.
+    The cross-build script supports an x86_64 GNU/Linux development host.
+    Browser tooling is excluded from the public source tree and releases.
+    The probe uses public fixture credentials and creates temporary identities
+    in memory. It does not open the root .env or use the canonical RSA key.