chore: lint core/react with eslint-plugin-react-hooks (#2192)

`eslint-plugin-react-hooks` was a `clients/web` devDependency only, and each
client's `eslint .` is scoped to its own directory — so the whole hook rule
set had never looked at `core/react/`, a directory of nothing but React
hooks. "Neither surface has JSX" was the stated reason and was never a good
one: the rules judge hooks, not JSX.

Add the plugin at the root and apply it in a `core/react/**` block (scoped
there rather than to all of `core/**`, since the rules key off the `use`
prefix), with `exhaustive-deps` promoted to `error` as `clients/web` does.

Resolve the 15 findings it then reports:

- `useSettingsDraft` / `useClientSettingsDraft` seed their draft during
  render instead of in a `targetId`/`opened`-keyed effect, so the previous
  target's values never reach the DOM — the same rule `clients/web` spells
  `useValueChange`. Their "latest value" refs move from render-time writes
  into an effect; every reader (the debounce timer, `flush`, `onChange`)
  runs after a commit, so a post-commit write is what they need.
- The three async loaders keep their effects behind justified inline
  disables: `set-state-in-effect` follows a call into an async function
  without modelling the `await`, verified against a minimal hook whose only
  setState is in a continuation.
- `useInitialConfig`'s cleanup bump keeps reading `generation.current` at
  teardown — the rule's "copy it into a variable" advice would restore a
  stale request token and let a superseded response commit.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013hzwzS8UvBsr4yZm7o7sev
Signed-off-by: cliffhall <cliff@futurescale.com>

eslint.config.js

@@ -1,5 +1,6 @@
 import js from "@eslint/js";
 import globals from "globals";
+import reactHooks from "eslint-plugin-react-hooks";
 import tseslint from "typescript-eslint";
 import { defineConfig, globalIgnores } from "eslint/config";
 
@@ -10,22 +11,25 @@ import { defineConfig, globalIgnores } from "eslint/config";
 // isomorphic TypeScript (browser-side OAuth + Node backends + shared runtime);
 // the shared surface is Node-only tooling/tests.
 //
-// ⚠️ There is no React plugin here, and "neither surface has JSX" is NOT a
-// sufficient reason for that — `core/react/` is a directory of React hooks,
-// which the hook rules judge whether or not any JSX is present. So the whole
-// `eslint-plugin-react-hooks` set, `set-state-in-effect` included, has never
-// looked at them: it is a devDependency of `clients/web` only, and Node
-// resolution walks up rather than down, so the root cannot even load it.
-// That is why the prop-into-effect re-sync #1955 fixed sat here unreported
-// while the identical shape is an error over in `clients/web/src`. Closing the
-// gap means adding the plugin at the root and taking what it then reports —
-// measured during #1955 as 15 findings, every one of them in a hook that issue
-// did not convert (the two settings-draft hooks and the three async fetch
-// hooks) and none in the 16 it did. Tracked on its own rather than folded in.
+// `core/react/` gets the React hook rules, and "neither surface has JSX" was
+// never a reason to withhold them — the hook rules judge hooks, not JSX, and
+// that directory is nothing but hooks. Until #2192 the whole
+// `eslint-plugin-react-hooks` set, `set-state-in-effect` included, had never
+// looked at them: the plugin was a devDependency of `clients/web` only, and
+// Node resolution walks up rather than down, so the root could not load it.
+// That is how the prop-into-effect re-sync #1955 fixed sat here unreported
+// while the identical shape was an error over in `clients/web/src`. The plugin
+// is now a root devDependency and the block below applies it.
 //
-// Type-aware linting for the two blocks below. `no-floating-promises` needs
-// type information, which `tseslint.configs.recommended` (the non-type-aware
-// set) does not provide — so each block adds a parser project (#1959).
+// Scoped to `core/react/**` rather than all of `core/**`: everything else
+// there is plain isomorphic TypeScript, and the rules key off the `use`-prefix
+// naming convention, so a non-React `useFoo` helper elsewhere in `core/` would
+// be judged as a hook it is not.
+//
+// Type-aware linting for the `core/` and shared surfaces below.
+// `no-floating-promises` needs type information, which
+// `tseslint.configs.recommended` (the non-type-aware set) does not provide —
+// so a block of its own adds a parser project (#1959).
 //
 // `tsconfig.lint.json` exists for this and nothing else: the root has no
 // tsconfig of its own (`core/` is typechecked through `clients/web`'s
@@ -81,6 +85,17 @@ export default defineConfig([
     },
     rules: sharedRules,
   },
+  {
+    // #2192. `exhaustive-deps` is promoted from the recommended set's `warn`
+    // for the same reason `clients/web` promotes it (#2085): `--max-warnings 0`
+    // already fails the gate on it, and matching the severity keeps an editor
+    // squiggle honest rather than depending on a CLI flag.
+    files: ["core/react/**/*.{ts,tsx}"],
+    extends: [reactHooks.configs.flat.recommended],
+    rules: {
+      "react-hooks/exhaustive-deps": "error",
+    },
+  },
   {
     files: [
       "test-servers/src/**/*.{ts,tsx,mts,cts}",