feat: add memory.patch, trim memory.get, unify the memory write path

memory.get no longer returns the embedding and content_tsv
----------------------------------------------------------
It used a bare select() and returned the raw DB row, while memory.list
and memory.search already projected an explicit 9-field shape. On a
~13k-char memory those two internal columns were 55% of the response
and pushed it past the MCP tool-output cap, so large memories could not
be fetched inline at all. memory.get now returns the same 9 fields as
its siblings; user_id is still selected for the authorization check and
stripped before responding.

memory.patch
------------
memory.update only accepts full replacement, so adding one line to a
large document meant resending the whole document — expensive enough
that edits were being skipped rather than risk silently truncating
shared team documents.

memory.patch replaces one exact occurrence of old_string. An absent or
ambiguous match is an error, never a silent no-op and never an
arbitrary pick; that refusal is what makes the operation safe to hand
to an agent. The semantics live in lib/memory-patch.ts as a pure
function, free of DB and auth, so both surfaces share them.

Shared mutation layer
---------------------
The MCP tools and the Web UI Server Actions each reimplemented
authorize -> mutate -> re-embed -> CAS -> audit, and had drifted. Both
now route through lib/memory-mutations.ts.

BEHAVIOUR CHANGE: memory.delete over MCP skipped the project ACL
whenever the caller authored the row, so a memory written while a share
was rw stayed deletable by its author after an owner downgraded that
share to ro. memory.update and the whole Web UI always checked.
Authoring a row now grants no standing write privilege on any path.

The one deliberate difference between the surfaces is injected as a
ProjectResolver: MCP refuses an unknown project key so an agent cannot
spawn near-miss projects off a typo, while the Web UI creates one
because a person typing a name into a form means to.

Tests and lint
--------------
Adds vitest. The integration tests run against a real Postgres rather
than a mocked DB. The embedder sidecar is the only stub and it is
deterministic per-text, so re-embedding is verified by asserting the
stored vector actually changed rather than that a mock was called. One
test pins that content_tsv is a generated column and therefore cannot
rot after a patch — only the embedding needs an explicit recompute.

pnpm lint previously dropped into an interactive `next lint` setup
prompt and exited 1; ESLint had never been configured here. Replaced
with the ESLint CLI and a flat config bridging eslint-config-next
through FlatCompat. Clean at --max-warnings=0.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/web/lib/memory-patch.ts

@@ -0,0 +1,76 @@
+import { MEMORY_CONTENT_MAX } from "@shared-memory/schemas";
+
+/**
+ * Pure string-level semantics for `memory.patch`.
+ *
+ * Kept free of any DB or auth dependency so both the MCP tool handler and
+ * the Web UI can share it, and so the refuse-rather-than-clobber rules
+ * below are directly testable.
+ *
+ * The contract mirrors the file-editing primitive coding agents already
+ * use: an `old_string` that is absent or ambiguous is an ERROR, never a
+ * silent no-op and never an arbitrary pick. That refusal is the property
+ * that makes the operation safe to hand to an agent editing a shared
+ * document it cannot afford to corrupt.
+ */
+export type PatchOutcome =
+  | { ok: true; content: string }
+  | { ok: false; error: string };
+
+function countOccurrences(haystack: string, needle: string): number {
+  let count = 0;
+  let from = 0;
+  for (;;) {
+    const at = haystack.indexOf(needle, from);
+    if (at === -1) return count;
+    count += 1;
+    // Advance past this match so overlapping matches aren't double-counted.
+    from = at + needle.length;
+  }
+}
+
+export function applyPatch(
+  content: string,
+  oldString: string,
+  newString: string,
+): PatchOutcome {
+  if (oldString === newString) {
+    return {
+      ok: false,
+      error: "old_string and new_string are identical; the patch would change nothing",
+    };
+  }
+
+  const first = content.indexOf(oldString);
+  if (first === -1) {
+    return {
+      ok: false,
+      error:
+        "old_string not found in the memory content; nothing was changed. Fetch the memory with memory.get and copy the exact text you mean to replace.",
+    };
+  }
+
+  // Only pay for a full count once we know there's more than one match.
+  if (content.indexOf(oldString, first + oldString.length) !== -1) {
+    const count = countOccurrences(content, oldString);
+    return {
+      ok: false,
+      error: `old_string matches ${count} times; it must match exactly once. Nothing was changed — include more surrounding context to identify the one you mean.`,
+    };
+  }
+
+  const patched =
+    content.slice(0, first) + newString + content.slice(first + oldString.length);
+
+  if (patched.length === 0) {
+    return { ok: false, error: "the patch would leave the memory empty" };
+  }
+  if (patched.length > MEMORY_CONTENT_MAX) {
+    return {
+      ok: false,
+      error: `the patched content would be ${patched.length.toLocaleString("en-US")} characters, over the ${MEMORY_CONTENT_MAX.toLocaleString("en-US")}-character limit`,
+    };
+  }
+
+  return { ok: true, content: patched };
+}