@@ -122,7 +122,8 @@ FOUNDATION_SRCS = \
     src/foundation/diagnostics.c \
     src/foundation/profile.c \
     src/foundation/dump_verify.c \
-    src/foundation/limits.c
+    src/foundation/limits.c \
+    src/foundation/subprocess.c
 
 # Existing extraction C code (compiled from current location)
 EXTRACTION_SRCS = \
@@ -182,7 +183,7 @@ STORE_SRCS = src/store/store.c
 CYPHER_SRCS = src/cypher/cypher.c
 
 # MCP server module (new)
-MCP_SRCS = src/mcp/mcp.c
+MCP_SRCS = src/mcp/mcp.c src/mcp/index_supervisor.c
 
 # Discover module (new)
 DISCOVER_SRCS = \
@@ -319,7 +320,8 @@ TEST_FOUNDATION_SRCS = \
     tests/test_log.c \
     tests/test_str_util.c \
     tests/test_platform.c \
-    tests/test_dump_verify.c
+    tests/test_dump_verify.c \
+    tests/test_subprocess.c
 
 TEST_EXTRACTION_SRCS = \
     tests/test_extraction.c \
 
@@ -14,6 +14,8 @@
 #include "lsp/rust_lsp.h"
 #include "preprocessor.h"
 #include "foundation/compat.h"
+#include "foundation/compat_fs.h"  // cbm_fopen — crash-supervisor per-file marker write
+#include "foundation/hash_table.h" // CBMHashTable — crash-supervisor quarantine set
 #include "tree_sitter/api.h" // TSParser, TSNode, TSTree, TSInput, TSLanguage, TSPoint, TSParseOptions, TSParseState
 #include "foundation/constants.h"
 #include "mimalloc.h" // mi_malloc/mi_calloc/mi_realloc/mi_free/mi_usable_size — bind 3rd-party allocators (#424)
@@ -566,6 +568,146 @@ static int count_params_from_signature(const char *sig) {
 
 // --- Main extraction function ---
 
+/* Test-only deterministic fault injection for the crash/hang supervisor tests.
+ * Gated entirely behind env vars that are never set in production; a matching
+ * rel_path either aborts (a fault signal the supervisor classifies as a crash)
+ * or spins forever (an external-scanner infinite loop the quiet-timeout kills).
+ * This gives an honest guard — green iff the supervisor actually contains a real
+ * fault — instead of a fixture that may stop faulting once a root cause is fixed. */
+/* Crash-supervisor per-file marker (Stage 3c skip-and-continue). In the
+ * supervisor's single-threaded recovery re-run, cbm_extract_file records the
+ * file it is ABOUT to process here (CBM_INDEX_MARKER_FILE) before touching it,
+ * so that if this file hard-crashes the worker the parent can read the marker
+ * back and learn the EXACT crasher to quarantine. Only meaningful single-
+ * threaded (parallel would race the marker); the env var is set solely by the
+ * supervisor during recovery, so it is a no-op on every normal run. */
+static void cbm_index_write_marker(const char *rel_path) {
+    const char *mf = getenv("CBM_INDEX_MARKER_FILE");
+    if (!mf || !mf[0] || !rel_path || !rel_path[0]) {
+        return;
+    }
+    FILE *f = cbm_fopen(mf, "wb");
+    if (f) {
+        (void)fputs(rel_path, f);
+        (void)fclose(f);
+    }
+}
+
+/* ── Crash-quarantine set (Stage 3c skip-and-continue) ──────────────────────
+ * After a crash the supervisor re-runs the worker single-threaded, passing
+ * CBM_INDEX_QUARANTINE_FILE — a newline-delimited list of repo-relative paths
+ * that already crashed the indexer and MUST NOT be extracted again. Owned here,
+ * next to the other env-driven extract hooks (marker + fault injector), so the
+ * single hard guard lives at the one choke point every pass funnels through
+ * (cbm_extract_file): whether a pass re-extracts from disk on a cache miss
+ * (sequential pass_calls/usages/semantic) or extracts fresh, a quarantined file
+ * short-circuits to an empty result and never reaches the parser/crash. The
+ * pipeline extract loops separately REPORT the skip as phase="crash" via
+ * cbm_index_is_quarantined() so the crasher surfaces in the response skipped[].
+ * Loaded once, lazily; read-only after load (safe for the parallel workers,
+ * though recovery runs single-threaded). Unset env ⇒ empty set ⇒ cheap no-op. */
+static CBMHashTable *g_quarantine_set = NULL;
+enum { CBM_QSET_UNINIT = 0, CBM_QSET_INITING = 1, CBM_QSET_INITED = 2 };
+static atomic_int g_quarantine_state = CBM_QSET_UNINIT;
+
+static void cbm_quarantine_load(void) {
+    const char *qf = getenv("CBM_INDEX_QUARANTINE_FILE");
+    if (!qf || !qf[0]) {
+        return; /* normal path: empty set */
+    }
+    FILE *f = cbm_fopen(qf, "rb");
+    if (!f) {
+        return;
+    }
+    CBMHashTable *set = cbm_ht_create(16);
+    if (!set) {
+        (void)fclose(f);
+        return;
+    }
+    char line[2048];
+    while (fgets(line, sizeof(line), f)) {
+        size_t len = strlen(line);
+        while (len > 0 && (line[len - 1] == '\n' || line[len - 1] == '\r')) {
+            line[--len] = '\0';
+        }
+        if (len == 0) {
+            continue;
+        }
+        /* Line format: "path\tphase" where phase is "crash" or "hang". A bare
+         * "path" line (no tab) is tolerated and defaults to phase "crash" for
+         * backward compatibility with older quarantine files. */
+        char *tab = strchr(line, '\t');
+        const char *phase = "crash";
+        if (tab) {
+            *tab = '\0';
+            if (tab[1]) {
+                phase = tab + 1;
+            }
+        }
+        if (line[0] == '\0') {
+            continue; /* empty path (line began with a tab) — skip */
+        }
+        /* The table borrows the key + value pointers, so dup both. Intentionally
+         * never freed: the set lives for the whole (short-lived worker) process.
+         * The value stores the phase so cbm_index_quarantine_phase() can report
+         * "crash" vs "hang"; membership (cbm_index_is_quarantined) is value != NULL. */
+        char *key = cbm_strdup(line);
+        char *pval = cbm_strdup(phase);
+        if (key && pval) {
+            cbm_ht_set(set, key, (void *)pval);
+        }
+    }
+    (void)fclose(f);
+    g_quarantine_set = set;
+}
+
+bool cbm_index_is_quarantined(const char *rel_path) {
+    if (!rel_path || !rel_path[0]) {
+        return false;
+    }
+    int state = atomic_load(&g_quarantine_state);
+    if (state != CBM_QSET_INITED) {
+        /* First caller wins the CAS and loads; racers spin until INITED.
+         * Same once-init pattern as cbm_ui_log_init (http_server.c). */
+        state = CBM_QSET_UNINIT;
+        if (atomic_compare_exchange_strong(&g_quarantine_state, &state, CBM_QSET_INITING)) {
+            cbm_quarantine_load();
+            atomic_store(&g_quarantine_state, CBM_QSET_INITED);
+        } else {
+            while (atomic_load(&g_quarantine_state) != CBM_QSET_INITED) {
+                cbm_usleep(1000); /* 1ms */
+            }
+        }
+    }
+    return g_quarantine_set && cbm_ht_has(g_quarantine_set, rel_path);
+}
+
+const char *cbm_index_quarantine_phase(const char *rel_path) {
+    /* cbm_index_is_quarantined drives the lazy once-load and returns true only
+     * when the set is loaded and holds rel_path — so on true, g_quarantine_set is
+     * non-NULL and the stored value is the phase string ("crash"/"hang"). */
+    if (!cbm_index_is_quarantined(rel_path)) {
+        return NULL;
+    }
+    return (const char *)cbm_ht_get(g_quarantine_set, rel_path);
+}
+
+static void cbm_test_fault_inject(const char *rel_path) {
+    if (!rel_path || !rel_path[0]) {
+        return;
+    }
+    const char *crash_on = getenv("CBM_TEST_CRASH_ON");
+    if (crash_on && crash_on[0] && strstr(rel_path, crash_on)) {
+        abort(); /* SIGABRT → WIFSIGNALED → classified as a crash */
+    }
+    const char *hang_on = getenv("CBM_TEST_HANG_ON");
+    if (hang_on && hang_on[0] && strstr(rel_path, hang_on)) {
+        for (;;) {
+            /* Busy-spin: the supervisor's quiet-timeout kills + reports us. */
+        }
+    }
+}
+
 CBMFileResult *cbm_extract_file(const char *source, int source_len, CBMLanguage language,
                                 const char *project, const char *rel_path, int64_t timeout_micros,
                                 const char **extra_defines, const char **include_paths) {
@@ -579,6 +721,20 @@ CBMFileResult *cbm_extract_file(const char *source, int source_len, CBMLanguage
     cbm_arena_init(&result->arena);
     CBMArena *a = &result->arena;
 
+    /* Crash-quarantine hard guard (Stage 3c): a file the supervisor pinned as a
+     * crasher must NEVER be parsed again. Return a clean empty result BEFORE the
+     * marker write and fault injector so no pass (including sequential re-extract
+     * passes that miss the result cache) can crash on it. The pipeline extract
+     * loops separately record it as a phase="crash" skip. Checked before the
+     * marker so quarantined files never overwrite it — the marker keeps pointing
+     * at the real (non-quarantined) file being processed when a crash hits. */
+    if (cbm_index_is_quarantined(rel_path)) {
+        return result;
+    }
+
+    cbm_index_write_marker(rel_path);
+    cbm_test_fault_inject(rel_path);
+
     // Get language spec
     const CBMLangSpec *spec = cbm_lang_spec(language);
     if (!spec) {
 
@@ -516,6 +516,20 @@ void cbm_alloc_init(void);
 // Initialize the library. Call once at startup. Returns 0 on success.
 int cbm_init(void);
 
+// True when rel_path is in the crash-quarantine set — the newline-delimited list
+// of files (CBM_INDEX_QUARANTINE_FILE) the crash supervisor pinned as crashers
+// during its single-threaded recovery re-run. Loaded once, lazily; read-only
+// after load. cbm_extract_file short-circuits such files to an empty result so no
+// pass can crash on them; the pipeline extract loops call this to also REPORT the
+// skip as phase="crash". Always false (cheap no-op) when the env var is unset.
+bool cbm_index_is_quarantined(const char *rel_path);
+
+// Phase a quarantined file was pinned under: "crash" (a fault signal) or "hang"
+// (killed for making no progress). Returns NULL when rel_path is not quarantined.
+// Drives the same lazy once-load as cbm_index_is_quarantined. Used by the pipeline
+// extract loops to report the skip's phase in skipped[] (falls back to "crash").
+const char *cbm_index_quarantine_phase(const char *rel_path);
+
 // Extract all data from one file. Caller must call cbm_free_result().
 // source must remain valid for the duration of the call.
 // timeout_micros: per-file parse timeout in microseconds (0 = no timeout).
 
@@ -8,6 +8,7 @@
 src/foundation/compat_fs.c:popen:cbm_popen wrapper definition (POSIX)
 src/foundation/compat_fs.c:cbm_popen:cbm_popen function definition
 src/foundation/compat_fs.c:fork:cbm_exec_no_shell — fork+execvp for shell-free subprocess execution
+src/foundation/subprocess.c:fork:cbm_run_posix — fork+execv for the crash/hang-isolating index worker (supervisor primitive; child execs immediately, no code runs in the forked image)
 src/foundation/compat_fs.c:execvp:cbm_exec_no_shell — direct exec without shell interpretation
 
 # ── CLI: update command (user-initiated, interactive) ──────────────────────