fix(writer): open the graph DB wide-safe for non-ASCII cache paths

cbm_writer_open used a raw ANSI-CP fopen for the hand-rolled SQLite
writer - the one file-creating call on the dump chain without a
UTF-8-to-wide conversion. On a non-ASCII Windows profile
(C:\Users\Kovacs Janos) extract and resolve succeeded but the dump
failed with pipeline.err phase=dump: fopen could not create graph.db
under the profile-derived cache dir while cbm_mkdir_p (already wide)
had happily created the directory around it. Routed through cbm_fopen,
matching #700 (pass readers) and #973 (canonicalization); POSIX is
byte-transparent.

New Windows guard test_non_ascii_cache_dump.py indexes an ASCII repo
into a non-ASCII CBM_CACHE_DIR and requires a query_graph readback
with Function count > 0 - proving the DB was written to and reopened
from the non-ASCII cache, not merely that no error surfaced. The
existing non-ASCII guard only varied the repo path against an ASCII
cache, which is why this class went unseen.

The USERPROFILE-sourced env encoding question (Layer 2 - _environ is
ANSI-CP, not UTF-8) is deliberately not bundled; it needs verification
on a real Windows box and will be filed separately if the guard alone
does not settle it.

Closes #996

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

internal/cbm/sqlite_writer.c

@@ -2211,7 +2211,11 @@ cbm_db_writer_t *cbm_writer_open(const char *path) {
      * -wal/-shm or a crashed session's WAL gets replayed on top of the
      * new file at the next open (#897). */
     cbm_remove_db_sidecars(path);
-    FILE *fp = fopen(path, "wb");
+    /* cbm_fopen, not raw fopen: the cache dir lives under the user profile,
+     * and an ANSI-CP fopen fails to create the DB on non-ASCII Windows
+     * profiles — the reported phase=dump failure (#996). Everything around
+     * this call (cbm_mkdir_p, sqlite3_open_v2 reopen) is already wide-safe. */
+    FILE *fp = cbm_fopen(path, "wb");
     if (!fp) {
         return NULL;
     }

scripts/test-windows.ps1

@@ -14,6 +14,7 @@
                     They must stay GREEN (exit 0); a RED (exit 1) means the fix
                     regressed and fails this runner.
                       * test_non_ascii_path.py    guards #636/#357 (fixed by #700)
+                      * test_non_ascii_cache_dump.py guards #996 (writer cbm_fopen)
                       * test_hook_augment.py      guards #618      (fixed by #619)
                       * test_ui_drive_listing.py  guards #548      (roots field)
                       * test_cli_non_ascii_arg.py guards #423/#20  (wide-argv main())
@@ -104,6 +105,7 @@ $env:CBM_INDEX_SUPERVISOR = "0" # in-process indexing (see .DESCRIPTION)
 # (exit 2) and is skipped rather than failed.
 $guards = @(
     "tests\windows\test_non_ascii_path.py",
+    "tests\windows\test_non_ascii_cache_dump.py",
     "tests\windows\test_hook_augment.py",
     "tests\windows\test_ui_drive_listing.py",
     "tests\windows\test_cli_non_ascii_arg.py"

tests/windows/test_non_ascii_cache_dump.py

@@ -0,0 +1,132 @@
+"""Regression guard for issue #996 — dump phase must write the graph DB into a
+NON-ASCII cache directory on Windows.
+
+The existing test_non_ascii_path.py exercises non-ASCII REPO paths against an
+ASCII cache, so it never covers the dump->cache write. #996's reporter (a
+non-ASCII %USERPROFILE%, e.g. C:\\Users\\Kovács János) saw extract/resolve
+succeed and `pipeline.err phase=dump`: cbm_writer_open used a raw ANSI-CP
+fopen for the hand-rolled SQLite writer (internal/cbm/sqlite_writer.c), the
+one file-creating call on the dump chain without UTF-8→wide conversion.
+Fixed by routing it through cbm_fopen (same pattern as #700/#973).
+
+This guard indexes an ASCII repo into a NON-ASCII cache dir (CBM_CACHE_DIR is
+read before any USERPROFILE derivation, so it isolates the writer cleanly).
+GREEN is non-vacuous: the index must succeed AND a query_graph readback must
+count Function nodes > 0 — proving the DB was written to and reopened from
+the non-ASCII cache, not merely that no error surfaced.
+
+Passes on Linux/macOS either way (byte-transparent UTF-8 filesystems).
+
+Exit code: 0 == invariant holds, 1 == regression, 2 == setup error.
+
+Usage:
+    python test_non_ascii_cache_dump.py <path-to-codebase-memory-mcp[.exe]>
+"""
+import json
+import os
+import shutil
+import sys
+import tempfile
+
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+from mcp_stdio import McpServer  # noqa: E402
+
+MATH_TS = (
+    "export function add(a: number, b: number): number { return a + b; }\n"
+    "export function mul(a: number, b: number): number { return add(a, a); }\n"
+    "export class Calc {\n"
+    "  total: number = 0;\n"
+    "  push(x: number): void { this.total = add(this.total, x); }\n"
+    "}\n"
+)
+
+# Mixed scripts in ONE segment — one shot covers the classes the sibling
+# test exercises separately (the writer either converts wide or it doesn't).
+NON_ASCII_CACHE_SEGMENT = "cache_café_Ωμέγα_日本語"
+
+
+def graph_function_count(server, project):
+    resp = server.call_tool(
+        "query_graph",
+        {
+            "project": project,
+            "format": "json",
+            "query": "MATCH (n:Function) RETURN count(n) AS c",
+        },
+    )
+    text, err = McpServer.tool_text(resp)
+    if err or not text:
+        return 0
+    data = json.loads(text)
+    rows = data.get("rows") or []
+    if not rows or not rows[0]:
+        return 0
+    return int(rows[0][0])
+
+
+def main():
+    if len(sys.argv) != 2:
+        print("usage: test_non_ascii_cache_dump.py <binary>")
+        return 2
+    binary = os.path.abspath(sys.argv[1])
+    if not os.path.exists(binary):
+        print(f"SETUP: binary not found: {binary}")
+        return 2
+
+    work = tempfile.mkdtemp(prefix="cbm_996_")
+    try:
+        repo = os.path.join(work, "ascii_repo")
+        os.makedirs(repo)
+        with open(os.path.join(repo, "math.ts"), "w", encoding="utf-8") as f:
+            f.write(MATH_TS)
+
+        cache = os.path.join(work, NON_ASCII_CACHE_SEGMENT)
+        os.makedirs(cache)
+
+        with McpServer(binary, cache_dir=cache) as s:
+            resp = s.call_tool("index_repository", {"repo_path": repo})
+            text, err = McpServer.tool_text(resp)
+            if err:
+                print(f"FAIL: index_repository rpc error: {err}")
+                return 1
+            text = text or ""
+            if '"error"' in text:
+                print(f"FAIL: index_repository into non-ASCII cache errored: {text[:300]}")
+                return 1
+            if "phase" in text and "dump" in text and "error" in text.lower():
+                print(f"FAIL: dump phase error: {text[:300]}")
+                return 1
+
+            # Non-vacuous readback: the DB must exist under the non-ASCII
+            # cache and answer queries.
+            project = None
+            try:
+                project = json.loads(text).get("project")
+            except (ValueError, AttributeError):
+                pass
+            if not project:
+                # TOON-shaped success output: fall back to list_projects.
+                lp = s.call_tool("list_projects", {})
+                lp_text, _ = McpServer.tool_text(lp)
+                lp_text = lp_text or ""
+                for line in lp_text.splitlines():
+                    if "ascii_repo" in line:
+                        project = line.split(",")[0].strip().strip('"')
+                        break
+            if not project:
+                print("FAIL: could not determine project name after index")
+                return 1
+
+            count = graph_function_count(s, project)
+            if count < 1:
+                print(f"FAIL: readback from non-ASCII cache found {count} Function nodes")
+                return 1
+
+        print(f"OK: dump wrote and reopened graph DB under non-ASCII cache ({count} functions)")
+        return 0
+    finally:
+        shutil.rmtree(work, ignore_errors=True)
+
+
+if __name__ == "__main__":
+    sys.exit(main())