xftp: implementation of XFTP client as web page

.gitignore

@@ -11,3 +11,4 @@ cabal.project.local~
 .hpc/
 *.tix
 .coverage
+

2026-02-04-xftp-web-persistent-connections.md

@@ -0,0 +1,53 @@
+# XFTPClientAgent Pattern
+
+## TOC
+1. Executive Summary
+2. Changes: client.ts
+3. Changes: agent.ts
+4. Changes: test/browser.test.ts
+5. Verification
+
+## Executive Summary
+
+Add `XFTPClientAgent` — a per-server connection pool matching the Haskell pattern. The agent caches `XFTPClient` instances by server URL. All orchestration functions (`uploadFile`, `downloadFile`, `deleteFile`) take `agent` as first parameter and use `getXFTPServerClient(agent, server)` instead of calling `connectXFTP` directly. Connections stay open on success; the caller creates and closes the agent.
+
+`connectXFTP` and `closeXFTP` stay exported (used by `XFTPWebTests.hs` Haskell tests). The `browserClients` hack, per-function `connections: Map`, and `getOrConnect` are deleted.
+
+## Changes: client.ts
+
+**Add** after types section: `XFTPClientAgent` interface, `newXFTPAgent`, `getXFTPServerClient`, `closeXFTPServerClient`, `closeXFTPAgent`.
+
+**Delete**: `browserClients` Map and all `isNode` browser-cache checks in `connectXFTP` and `closeXFTP`.
+
+**Revert `closeXFTP`** to unconditional `c.transport.close()` (browser transport.close() is already a no-op).
+
+`connectXFTP` stays exported (backward compat) but becomes a raw low-level function — no caching.
+
+## Changes: agent.ts
+
+**Imports**: replace `connectXFTP`/`closeXFTP` with `getXFTPServerClient`/`closeXFTPAgent` etc.
+
+**Re-export** from agent.ts: `newXFTPAgent`, `closeXFTPAgent`, `XFTPClientAgent`.
+
+**`uploadFile`**: add `agent: XFTPClientAgent` as first param. Replace `connectXFTP` → `getXFTPServerClient`. Remove `finally { closeXFTP }`. Pass `agent` to `uploadRedirectDescription`.
+
+**`uploadRedirectDescription`**: change from `(client, server, innerFd)` to `(agent, server, innerFd)`. Get client via `getXFTPServerClient`.
+
+**`downloadFile`**: add `agent` param. Delete local `connections: Map`. Replace `getOrConnect` → `getXFTPServerClient`. Remove finally cleanup. Pass `agent` to `downloadWithRedirect`.
+
+**`downloadWithRedirect`**: add `agent` param. Same replacements. Remove try/catch cleanup. Recursive call passes `agent`.
+
+**`deleteFile`**: add `agent` param. Same pattern.
+
+**Delete**: `getOrConnect` function entirely.
+
+## Changes: test/browser.test.ts
+
+Create agent before operations, pass to upload/download, close in finally.
+
+## Verification
+
+1. `npx vitest --run` — browser round-trip test passes
+2. No remaining `browserClients`, `getOrConnect`, or per-function `connections: Map` locals
+3. `connectXFTP` and `closeXFTP` still exported (XFTPWebTests.hs compat)
+4. All orchestration functions take `agent` as first param

contributing/CODE.md

@@ -2,7 +2,17 @@
 
 This file provides guidance on coding style and approaches and on building the code.
 
-## Code Style and Formatting
+## Code Security
+
+When designing code and planning implementations:
+- Apply adversarial thinking, and consider what may happen if one of the communicating parties is malicious.
+- Formulate an explicit threat model for each change - who can do which undesirable things and under which circumstances.
+
+## Code Quality Standards
+
+Haskell client and server code serves as system specification, not just implementation — we use type-driven design to reflect the business domain in types. Quality, conciseness, and clarity of Haskell code are critical.
+
+## Code Style, Formatting and Approaches
 
 The project uses **fourmolu** for Haskell code formatting. Configuration is in `fourmolu.yaml`.
 
@@ -41,6 +51,11 @@ Some files that use CPP language extension cannot be formatted as a whole, so in
 - Never do refactoring unless it substantially reduces cost of solving the current problem, including the cost of refactoring
 - Aim to minimize the code changes - do what is minimally required to solve users' problems
 
+**Document and code structure:**
+- **Never move existing code or sections around** - add new content at appropriate locations without reorganizing existing structure.
+- When adding new sections to documents, continue the existing numbering scheme.
+- Minimize diff size - prefer small, targeted changes over reorganization.
+
 **Code analysis and review:**
 - Trace data flows end-to-end: from origin, through storage/parameters, to consumption. Flag values that are discarded and reconstructed from partial data (e.g. extracted from a URI missing original fields) — this is usually a bug.
 - Read implementations of called functions, not just signatures — if duplication involves a called function, check whether decomposing it resolves the duplication.