Zero C-compiler warnings on all three architectures; fix real restore_vm_state() bug

Maintainability sweep (prompted by "this is getting hard to maintain"):
fixed the remaining three warning classes after the missing-field-
initializers commit -- 2x -Wsign-compare (control_words.c, cast at the
comparison site rather than changing cf_last_mode's type, which
deliberately holds a -999 sentinel outside vm_mode_t's valid range),
2x -Wstringop-truncation (mkcapsule.c, strncpy+manual-null-terminate
replaced with the idiomatic snprintf equivalent), and 26x
-Wunused-parameter (mostly documented stubs, silenced with the repo's
existing (void)param; idiom).

One of the unused-parameter warnings was not a deliberate stub -- a
real bug. restore_vm_state() (test_common.c) is named, documented, and
called by nine real call sites (acl_words_test.c x8 plus its own
internal use) as "restore saved VM state", but ignored all four of its
parameters and hard-reset to a fixed baseline instead, silently not
restoring what any caller actually saved. Fixed to actually assign the
passed-in dsp/rsp/error/mode. Found while fixing warnings, reported
before touching it, fixed/tested/documented/committed on explicit
instruction.

Verified: all three architectures build with zero C-compiler warnings
(amd64: 3040 -> 0; aarch64's one remaining note is lld-link's own
unrelated linker warning, not a C warning). Full amd64 acceptance boot
post-fix: POST 1003/965/0/0/38 (total/passed/failed/errors/stubs),
"ALL IMPLEMENTED TESTS PASSED!", contract checks (A4'/A1) all passed,
dict_hash=0x24b4279f0670aa3a -- an exact match to this document's own
previously-recorded baseline hash.

.claude/CLAUDE.md corrected to describe the real -Wno-error= exemption
list instead of the "-Wall -Werror" oversimplification. FABRIC-2.md
Section J records the full sweep, including doc-tree staleness findings
flagged but not fixed this pass (docs/lithosananke/ROADMAP.md branch
topology, docs/03-architecture/word-acl/DESIGN.md's Phase 7 claim
contradicting CLAUDE.md, top-level ROADMAP.md's stale StarForth-era
status, the Isabelle pipeline-metrics model mismatch).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/inference_engine.c

@@ -443,6 +443,7 @@ uint32_t find_variance_inflection(
     q48_16_t full_variance  /* Unused in new algorithm */
 )
 {
+    (void)full_variance;
     /* ========================================================================
      * REDESIGNED: Levene's Test for Statistical Validity (2025-11-19)
      * ========================================================================
@@ -632,6 +633,8 @@ static uint64_t compute_fit_quality(
     uint64_t slope_q48
 )
 {
+    (void)heat_data;
+    (void)slope_q48;
     if (length < 2) {
         return q48_from_u64(1);  /* Perfect fit if no data */
     }

src/physics_pipelining_metrics.c

@@ -735,6 +735,8 @@ char *transition_metrics_context_accuracy_string(const WordTransitionMetrics *me
 uint32_t transition_metrics_binary_chop_suggest_window(const WordTransitionMetrics *metrics,
                                                        uint32_t current_window,
                                                        double accuracy_at_current) {
+    (void)metrics;
+    (void)accuracy_at_current;
     /* Phase 1: Stub - just return doubled window size per user's request
      * Phase 2 will implement actual binary chop search:
      *   - Start at window=2

src/test_runner/test_common.c

@@ -147,13 +147,16 @@ void save_vm_state(VM* vm, int* dsp, int* rsp, int* error, vm_mode_t* mode)
  */
 void restore_vm_state(VM* vm, int dsp, int rsp, int error, vm_mode_t mode)
 {
-    /* For stress tests and error recovery, aggressively clear both stacks
-     * to prevent any stale state from affecting subsequent tests.
-     * This is safer than trying to selectively clear ranges. */
-    vm->dsp = -1;
-    vm->rsp = -1;
-    vm->error = 0;
-    vm->mode = MODE_INTERPRET;
+    /* Restore to the caller-supplied saved state -- every real caller
+     * (acl_words_test.c, this file's own save/restore pairs) captures
+     * dsp/rsp/error/mode before running a test specifically so it can be
+     * put back here. This previously ignored all four parameters and
+     * hard-reset to a fixed baseline instead, silently not restoring
+     * anything callers actually saved. */
+    vm->dsp = dsp;
+    vm->rsp = rsp;
+    vm->error = error;
+    vm->mode = mode;
 
     /* Clear control flow flags to prevent stale state between tests */
     vm->exit_colon = 0;

src/test_runner/test_runner.c

@@ -254,6 +254,7 @@ void run_module_tests(VM *vm, const char *module_name) {
  * @param word_name Name of the Forth word to test
  */
 void run_word_tests(VM *vm, const char *word_name) {
+    (void)vm;
     log_message(LOG_INFO, "Searching for tests for word: %s", word_name);
 
     int found = 0;

src/word_source/control_words.c

@@ -124,7 +124,7 @@ static inline void cf_epoch_sync(VM *vm) {
         cf_last_mode = vm->mode;
         return;
     }
-    if (vm->mode != cf_last_mode) {
+    if ((int)vm->mode != cf_last_mode) {
         cf_sp = -1;
         cf_last_mode = vm->mode;
         log_message(LOG_DEBUG, "CF: reset (mode transition)");

src/word_source/io_words.c

@@ -71,6 +71,7 @@ static void io_word_emit(VM *vm) {
  *          Outputs a newline character to the terminal
  */
 static void io_word_cr(VM *vm) {
+    (void)vm;
     putchar('\n');
     fflush(stdout);
 }
@@ -146,6 +147,7 @@ static void io_word_type(VM *vm) {
  *          Outputs a single space character to terminal
  */
 static void io_word_space(VM *vm) {
+    (void)vm;
     putchar(' ');
     fflush(stdout);
 }

src/word_source/string_words.c

@@ -334,6 +334,7 @@ void string_word_bracket_tick(VM *vm) {
 
 /* LITERAL / [LITERAL] are placeholders here */
 void string_word_literal(VM *vm) {
+    (void)vm;
 }
 
 void string_word_bracket_literal(VM *vm) { string_word_literal(vm); }