/*
 * test_complexity.c — Complexity guard: superlinearity detection at tiny input
 *                     sizes, gated on DETERMINISTIC work counters — never time.
 *
 * Why this suite exists: the v0.9.0→v0.10.x indexing regression was a
 * files×corpus_defs coupling in cross-file LSP (#1669). Finding it took an
 * 11-corpus A/B across two release binaries, because nothing in CI could see
 * an O(n^2) forming. This suite makes that class of bug fail a unit test.
 *
 * Method — replicated independent modules:
 *   Build a synthetic corpus of k INDEPENDENT module copies per language
 *   (module i never references module j). Then every extensive quantity —
 *   nodes, edges, and Σ per-file work — MUST grow linearly in k. Run the full
 *   in-process pipeline at k and 2k and assert counter RATIOS:
 *
 *       linear pipeline    ratio ≈ 2      (gate: within [lo, hi])
 *       files×corpus bug   ratio ≈ 4      (per-file work itself grows with k)
 *
 *   Ratios expose the exponent at TINY sizes (dozens of files, seconds of
 *   runtime): a counter that counts the quadratic term directly doubles its
 *   growth per doubling regardless of absolute scale. No large corpora needed.
 *
 * Determinism doctrine (O9): a verdict must be a pure function of
 * (code, input). Work counters are sums over per-file work and do not depend
 * on scheduling; wall time does. Therefore ONLY counters gate. Throughput
 * (nodes/s, edges/s) is measured and written to a LOCAL report under private/
 * as information for trend comparison — it never gates, and the report step is
 * skipped entirely under CBM_SKIP_PERF (starved fidelity legs would record
 * meaningless rates).
 *
 * Dynamic coverage: languages come from two providers, iterated over the full
 * CBM_LANG_COUNT enum —
 *   1. embedded templates below (the LSP-hybrid languages, where cross-file
 *      machinery — and therefore files×corpus coupling risk — lives);
 *   2. auto-discovered fixture dirs tests/fixtures/complexity/<lang-name>/
 *      (drop files there when adding a language; no test edit needed).
 * Languages with neither provider are recorded in the report as skipped with
 * the reason "no complexity template": their extractors are per-file by
 * construction (grammar-only, no cross-file resolution), so the coupling this
 * suite hunts cannot arise from them; the shared passes they feed (registry,
 * similarity, semantic) are exercised by the template corpus.
 */
#include "test_framework.h"
#include "test_helpers.h"

#include "../src/foundation/compat.h"
#include "../src/foundation/compat_fs.h"
#include "../src/foundation/log.h"
#include "../src/foundation/profile.h"
#include "cbm.h"
#include "discover/discover.h"
#include "pipeline/pass_lsp_cross.h"
#include "pipeline/pipeline.h"
#include "pipeline/pipeline_internal.h"
#include "store/store.h"

#include <stdatomic.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* Tail-match scan counters (defined in pass_parallel.c, declared in
 * lsp_resolve.h — re-declared here to avoid pulling that header's statics). */
extern _Atomic uint64_t g_lsp_tail_lookups;
extern _Atomic uint64_t g_lsp_tail_candidates;

/* ── Corpus scale ──────────────────────────────────────────────────────
 * Small on purpose: the gate reads exponents from ratios, not magnitudes.
 * K_BASE modules vs 2*K_BASE modules, CX_FILES_PER_MOD files each, per
 * provider language. Total runtime target for the whole suite: seconds. */
enum {
    CX_K_BASE = 3,
    CX_FILES_PER_MOD = 5,
    /* Gate only when the base run produced enough work for the ratio to be
     * meaningful — a near-zero denominator would make the gate noise. The
     * false-guard audit rule applies: a separate assertion below proves the
     * counter is genuinely nonzero so this gate can never pass vacuously. */
    CX_MIN_BASE_WORK = 40,
    /* The pipeline resolves sequentially below MIN_FILES_FOR_PARALLEL (50
     * files, pipeline.c) and that path builds no shared registries — so both
     * legs of every corpus pair must exceed it or the gates measure the wrong
     * code path. The sequential path's own per-file registry work is bounded
     * by the 50-file ceiling and is deliberately out of scope here. */
    CX_BIGPKG_FILES_PER_K = 20,
};

/* Linear growth bounds for a 2x input doubling. Fixed structural overhead
 * (Project/root nodes) pulls node ratios slightly under 2; template boundary
 * effects push edge ratios slightly around 2. A files×corpus coupling lands
 * at ~4 — far outside. */
#define CX_RATIO_LO 1.45
#define CX_RATIO_HI 2.75

/* ── Language templates ────────────────────────────────────────────────
 * Each emitter writes file j of a module. Files reference file j-1 of the
 * SAME module (cross-file resolution work); modules never reference each
 * other (independence — the property the linearity gate rests on). */

static void cx_emit_java(FILE *f, int m, int j) {
    fprintf(f, "package mod%d;\n\npublic class C%d {\n", m, j);
    fprintf(f, "    public int val%d(int x) {\n        return x + %d;\n    }\n", j, j);
    if (j > 0) {
        fprintf(f, "    public int chain() {\n");
        fprintf(f, "        C%d prev = new C%d();\n", j - 1, j - 1);
        fprintf(f, "        return prev.val%d(1) + val%d(2);\n    }\n", j - 1, j);
    } else {
        fprintf(f, "    public int chain() {\n        return val0(2);\n    }\n");
    }
    fprintf(f, "}\n");
}

static void cx_emit_python(FILE *f, int m, int j) {
    (void)m;
    if (j > 0) {
        fprintf(f, "import f%d\n\n", j - 1);
    }
    fprintf(f, "def val%d(x):\n    return x + %d\n\n", j, j);
    if (j > 0) {
        fprintf(f, "def chain%d():\n    return f%d.val%d(1) + val%d(2)\n", j, j - 1, j - 1, j);
    } else {
        fprintf(f, "def chain0():\n    return val0(2)\n");
    }
}

static void cx_emit_go(FILE *f, int m, int j) {
    fprintf(f, "package mod%d\n\n", m);
    fprintf(f, "func Val%d(x int) int {\n\treturn x + %d\n}\n\n", j, j);
    if (j > 0) {
        fprintf(f, "func Chain%d() int {\n\treturn Val%d(1) + Val%d(2)\n}\n", j, j - 1, j);
    } else {
        fprintf(f, "func Chain0() int {\n\treturn Val0(2)\n}\n");
    }
}

static void cx_emit_ts(FILE *f, int m, int j) {
    (void)m;
    if (j > 0) {
        fprintf(f, "import { val%d } from \"./f%d\";\n\n", j - 1, j - 1);
    }
    fprintf(f, "export function val%d(x: number): number {\n    return x + %d;\n}\n\n", j, j);
    if (j > 0) {
        fprintf(f, "export function chain%d(): number {\n    return val%d(1) + val%d(2);\n}\n", j,
                j - 1, j);
    } else {
        fprintf(f, "export function chain0(): number {\n    return val0(2);\n}\n");
    }
}

typedef struct {
    CBMLanguage lang;
    const char *dirname; /* corpus subdir, doubles as the per-lang scope */
    const char *file_prefix;
    const char *ext;
    void (*emit)(FILE *f, int m, int j);
} CxTemplate;

static const CxTemplate CX_TEMPLATES[] = {
    {CBM_LANG_JAVA, "javasrc", "C", ".java", cx_emit_java},
    {CBM_LANG_PYTHON, "pysrc", "f", ".py", cx_emit_python},
    {CBM_LANG_GO, "gosrc", "f", ".go", cx_emit_go},
    {CBM_LANG_TYPESCRIPT, "tssrc", "f", ".ts", cx_emit_ts},
};
enum { CX_TEMPLATE_COUNT = sizeof(CX_TEMPLATES) / sizeof(CX_TEMPLATES[0]) };

/* Fixture-dir provider: tests/fixtures/complexity/<lang-name>/ — every file in
 * it is copied verbatim into each module dir. Lets a new language join the
 * guard by dropping fixtures, with no edit to this suite. */
static bool cx_fixture_dir_for(CBMLanguage lang, char *out, size_t cap) {
    const char *name = cbm_language_name(lang);
    if (!name || !name[0]) {
        return false;
    }
    snprintf(out, cap, "tests/fixtures/complexity/%s", name);
    cbm_dir_t *d = cbm_opendir(out);
    if (!d) {
        return false;
    }
    cbm_closedir(d);
    return true;
}

static int cx_copy_file(const char *src, const char *dst) {
    FILE *in = fopen(src, "rb");
    if (!in) {
        return -1;
    }
    FILE *out = fopen(dst, "wb");
    if (!out) {
        fclose(in);
        return -1;
    }
    char buf[4096];
    size_t n;
    while ((n = fread(buf, 1, sizeof(buf), in)) > 0) {
        fwrite(buf, 1, n, out);
    }
    fclose(in);
    fclose(out);
    return 0;
}

/* ── Corpus builder ──────────────────────────────────────────────────── */

static int cx_build_corpus(const char *root, int k_modules) {
    char dir[1024];
    char path[1200];
    for (int t = 0; t < CX_TEMPLATE_COUNT; t++) {
        const CxTemplate *tp = &CX_TEMPLATES[t];
        for (int m = 0; m < k_modules; m++) {
            snprintf(dir, sizeof(dir), "%s/%s/mod%d", root, tp->dirname, m);
            if (th_mkdir_p(dir) != 0) {
                return -1;
            }
            for (int j = 0; j < CX_FILES_PER_MOD; j++) {
                snprintf(path, sizeof(path), "%s/%s%d%s", dir, tp->file_prefix, j, tp->ext);
                FILE *f = fopen(path, "w");
                if (!f) {
                    return -1;
                }
                tp->emit(f, m, j);
                fclose(f);
            }
        }
    }
    /* Fixture-dir providers: replicate each discovered language dir into
     * k module copies. Distinct paths make distinct modules/QNs, which is all
     * the independence argument needs. */
    for (int lang = 0; lang < CBM_LANG_COUNT; lang++) {
        bool templated = false;
        for (int t = 0; t < CX_TEMPLATE_COUNT; t++) {
            if (CX_TEMPLATES[t].lang == (CBMLanguage)lang) {
                templated = true;
            }
        }
        if (templated) {
            continue;
        }
        char fixdir[512];
        if (!cx_fixture_dir_for((CBMLanguage)lang, fixdir, sizeof(fixdir))) {
            continue;
        }
        cbm_dir_t *d = cbm_opendir(fixdir);
        if (!d) {
            continue;
        }
        cbm_dirent_t *entry;
        while ((entry = cbm_readdir(d)) != NULL) {
            if (entry->name[0] == '.') {
                continue;
            }
            for (int m = 0; m < k_modules; m++) {
                snprintf(dir, sizeof(dir), "%s/fx_%s/mod%d", root,
                         cbm_language_name((CBMLanguage)lang), m);
                if (th_mkdir_p(dir) != 0) {
                    continue;
                }
                char src[1024];
                snprintf(src, sizeof(src), "%s/%s", fixdir, entry->name);
                snprintf(path, sizeof(path), "%s/%s", dir, entry->name);
                (void)cx_copy_file(src, path);
            }
        }
        cbm_closedir(d);
    }
    return 0;
}

/* Corpus shape #2 — the growing shared package. Real monorepos concentrate
 * files in a few large packages (org.<org>.common, …), and the JVM filter
 * branch includes every def sharing the file's namespace — so per-file work
 * tracks PACKAGE size. A package whose file count scales with the corpus is
 * therefore the honest reproducer for the #1669 growth pattern that fully
 * independent modules cannot show: here every extensive quantity must STILL
 * be linear in k, while a namespace/module-scoped per-file registry build
 * goes quadratic. */
static int cx_build_bigpkg(const char *root, int k) {
    char dir[1024];
    char path[1200];
    snprintf(dir, sizeof(dir), "%s/bigsrc/bigpkg", root);
    if (th_mkdir_p(dir) != 0) {
        return -1;
    }
    int files = k * CX_BIGPKG_FILES_PER_K;
    for (int j = 0; j < files; j++) {
        snprintf(path, sizeof(path), "%s/B%d.java", dir, j);
        FILE *f = fopen(path, "w");
        if (!f) {
            return -1;
        }
        fprintf(f, "package bigpkg;\n\npublic class B%d {\n", j);
        fprintf(f, "    public int val%d(int x) {\n        return x + %d;\n    }\n", j, j);
        if (j > 0) {
            fprintf(f, "    public int chain() {\n");
            fprintf(f, "        B%d prev = new B%d();\n", j - 1, j - 1);
            fprintf(f, "        return prev.val%d(1) + val%d(2);\n    }\n", j - 1, j);
        } else {
            fprintf(f, "    public int chain() {\n        return val0(2);\n    }\n");
        }
        fprintf(f, "}\n");
        fclose(f);
    }
    return 0;
}

/* ── Metrics ─────────────────────────────────────────────────────────── */

/* Per-pass timing capture: a TEE log sink parses `pass.timing` lines during a
 * run. Information for the report only — pass timings are wall-clock and never
 * gate (O9). */
enum { CX_MAX_PASSES = 48 };
typedef struct {
    char name[64];
    long ms;
} CxPassMs;
static CxPassMs g_cx_passes[CX_MAX_PASSES];
static _Atomic int g_cx_pass_count = 0;

static void cx_pass_sink(const char *line) {
    if (!line || !strstr(line, "pass.timing")) {
        return;
    }
    const char *pp = strstr(line, "pass=");
    const char *ee = strstr(line, "elapsed_ms=");
    if (!pp || !ee) {
        return;
    }
    int n = atomic_fetch_add_explicit(&g_cx_pass_count, 1, memory_order_relaxed);
    if (n >= CX_MAX_PASSES) {
        return;
    }
    size_t i = 0;
    pp += 5;
    while (pp[i] && pp[i] != ' ' && i < sizeof(g_cx_passes[n].name) - 1) {
        g_cx_passes[n].name[i] = pp[i];
        i++;
    }
    g_cx_passes[n].name[i] = '\0';
    g_cx_passes[n].ms = atol(ee + 11);
}

typedef struct {
    int nodes;
    int edges;
    int lang_nodes[CX_TEMPLATE_COUNT];
    int lang_edges[CX_TEMPLATE_COUNT];
    CxPassMs passes[CX_MAX_PASSES];
    int pass_count;
    uint64_t perfile_defs; /* Σ defs registered by per-file/overlay registry builds */
    uint64_t build_files;
    uint64_t filter_failed;
    uint64_t tail_lookups;
    uint64_t tail_candidates;
    uint64_t fallback_rows;
    double wall_s;
} CxMetrics;

static double cx_now_s(void) {
    struct timespec ts;
    cbm_profile_now(&ts);
    return (double)ts.tv_sec + (double)ts.tv_nsec / 1e9;
}

static int cx_run(const char *root, const char *db_path, CxMetrics *out) {
    memset(out, 0, sizeof(*out));

    uint64_t d0;
    uint64_t b0;
    uint64_t f0;
    uint64_t x0;
    cbm_pxc_filter_stats(&d0, &b0, &f0, &x0);
    uint64_t tl0 = atomic_load_explicit(&g_lsp_tail_lookups, memory_order_relaxed);
    uint64_t tc0 = atomic_load_explicit(&g_lsp_tail_candidates, memory_order_relaxed);
    uint64_t fb0 = cbm_pp_lsp_linear_fallback_rows();

    atomic_store_explicit(&g_cx_pass_count, 0, memory_order_relaxed);
    cbm_log_set_sink_ex(cx_pass_sink, CBM_LOG_SINK_TEE);

    double t0 = cx_now_s();
    cbm_pipeline_t *p = cbm_pipeline_new(root, db_path, CBM_MODE_FULL);
    if (!p) {
        return -1;
    }
    int rc = cbm_pipeline_run(p);
    out->wall_s = cx_now_s() - t0;
    cbm_log_set_sink(NULL);
    int captured = atomic_load_explicit(&g_cx_pass_count, memory_order_relaxed);
    out->pass_count = captured < CX_MAX_PASSES ? captured : CX_MAX_PASSES;
    memcpy(out->passes, g_cx_passes, (size_t)out->pass_count * sizeof(CxPassMs));

    char project[512];
    snprintf(project, sizeof(project), "%s", cbm_pipeline_project_name(p));
    cbm_pipeline_free(p);
    if (rc != 0) {
        return rc;
    }

    uint64_t d1;
    uint64_t b1;
    uint64_t f1;
    uint64_t x1;
    cbm_pxc_filter_stats(&d1, &b1, &f1, &x1);
    out->perfile_defs = d1 - d0;
    out->build_files = b1 - b0;
    out->filter_failed = x1 - x0;
    out->tail_lookups = atomic_load_explicit(&g_lsp_tail_lookups, memory_order_relaxed) - tl0;
    out->tail_candidates = atomic_load_explicit(&g_lsp_tail_candidates, memory_order_relaxed) - tc0;
    out->fallback_rows = cbm_pp_lsp_linear_fallback_rows() - fb0;

    cbm_store_t *s = cbm_store_open_path(db_path);
    if (!s) {
        return -1;
    }
    out->nodes = cbm_store_count_nodes(s, project);
    out->edges = cbm_store_count_edges(s, project);
    for (int t = 0; t < CX_TEMPLATE_COUNT; t++) {
        out->lang_nodes[t] = cbm_store_count_nodes_scoped(s, project, CX_TEMPLATES[t].dirname);
        out->lang_edges[t] = cbm_store_count_edges_scoped(s, project, CX_TEMPLATES[t].dirname);
    }
    cbm_store_close(s);
    return 0;
}

static double cx_ratio(double num, double den) {
    return den > 0.0 ? num / den : 0.0;
}

/* Shared across the suite so the report test reuses the measured pair instead
 * of paying two more pipeline runs. */
static CxMetrics g_cx_base;
static CxMetrics g_cx_doubled;
static bool g_cx_measured = false;
static char g_cx_root_base[512];
static char g_cx_root_doubled[512];

static int cx_measure_pair(void) {
    if (g_cx_measured) {
        return 0;
    }
    const char *tmp = cbm_tmpdir();
    snprintf(g_cx_root_base, sizeof(g_cx_root_base), "%s/cbm_cx_base_XXXXXX", tmp);
    snprintf(g_cx_root_doubled, sizeof(g_cx_root_doubled), "%s/cbm_cx_dbl_XXXXXX", tmp);
    if (!cbm_mkdtemp(g_cx_root_base) || !cbm_mkdtemp(g_cx_root_doubled)) {
        return -1;
    }
    if (cx_build_corpus(g_cx_root_base, CX_K_BASE) != 0 ||
        cx_build_corpus(g_cx_root_doubled, CX_K_BASE * 2) != 0) {
        return -1;
    }
    char db1[600];
    char db2[600];
    snprintf(db1, sizeof(db1), "%s/cx.db", g_cx_root_base);
    snprintf(db2, sizeof(db2), "%s/cx.db", g_cx_root_doubled);
    if (cx_run(g_cx_root_base, db1, &g_cx_base) != 0) {
        return -1;
    }
    if (cx_run(g_cx_root_doubled, db2, &g_cx_doubled) != 0) {
        return -1;
    }
    g_cx_measured = true;
    return 0;
}

/* ── Tests ───────────────────────────────────────────────────────────── */

/* The flagship gate. Independent module copies ⇒ every extensive quantity must
 * scale linearly in the copy count. A files×corpus coupling shows up as a
 * ratio near 4 on the counter that sums per-file work. */
TEST(complexity_replicated_modules_scale_linearly) {
    if (cx_measure_pair() != 0) {
        FAIL("failed to build/run the complexity corpus pair");
    }
    const CxMetrics *a = &g_cx_base;
    const CxMetrics *b = &g_cx_doubled;

    /* Sanity: the corpus is real. */
    ASSERT_GT(a->nodes, 50);
    ASSERT_GT(a->edges, 20);

    double node_r = cx_ratio(b->nodes, a->nodes);
    double edge_r = cx_ratio(b->edges, a->edges);
    printf("    nodes %d -> %d (ratio %.2f)  edges %d -> %d (ratio %.2f)\n", a->nodes, b->nodes,
           node_r, a->edges, b->edges, edge_r);
    ASSERT_TRUE(node_r >= CX_RATIO_LO && node_r <= CX_RATIO_HI);
    ASSERT_TRUE(edge_r >= CX_RATIO_LO && edge_r <= CX_RATIO_HI);

    /* Per-language linearity, from the same run pair (scoped by subtree). If
     * scoped counting returns 0 for the base run the scope semantics changed —
     * surface that rather than silently skipping. */
    for (int t = 0; t < CX_TEMPLATE_COUNT; t++) {
        ASSERT_GT(a->lang_nodes[t], 0);
        double lr = cx_ratio(b->lang_nodes[t], a->lang_nodes[t]);
        printf("    %-8s nodes %d -> %d (ratio %.2f)\n", CX_TEMPLATES[t].dirname, a->lang_nodes[t],
               b->lang_nodes[t], lr);
        ASSERT_TRUE(lr >= CX_RATIO_LO && lr <= CX_RATIO_HI);
    }
    PASS();
}

/* Σ per-file registry work must be linear in independent copies. This is the
 * counter that measured ~4x/doubling on the v0.10.x Java path (defs_per_file
 * tracked defs_total — #1669). Guarded against vacuous passes: the base run
 * must have produced real registry work, so an accidental zeroing of the
 * counter fails loudly instead of green-washing the gate. */
TEST(complexity_perfile_registry_work_is_linear) {
    if (cx_measure_pair() != 0) {
        FAIL("failed to build/run the complexity corpus pair");
    }
    const CxMetrics *a = &g_cx_base;
    const CxMetrics *b = &g_cx_doubled;

    printf("    perfile_defs %llu -> %llu  build_files %llu -> %llu  filter_failed %llu\n",
           (unsigned long long)a->perfile_defs, (unsigned long long)b->perfile_defs,
           (unsigned long long)a->build_files, (unsigned long long)b->build_files,
           (unsigned long long)(a->filter_failed + b->filter_failed));

    /* Non-vacuous: the corpus includes languages that register per-file defs
     * (Java at minimum). If this is ever 0 the counter wiring broke — that is
     * a test defect to fix, not a pass. */
    ASSERT_GT((long long)a->perfile_defs, (long long)CX_MIN_BASE_WORK);

    double defs_r = cx_ratio((double)b->perfile_defs, (double)a->perfile_defs);
    printf("    perfile_defs ratio %.2f (linear ~2, files x corpus ~4)\n", defs_r);
    ASSERT_TRUE(defs_r <= CX_RATIO_HI);

    /* Recorded, deliberately NOT gated (the O10 note): tail_candidates and
     * fallback_rows are legitimately superlinear under replication TODAY —
     * same-short-name candidate sets grow with the copy count by design of
     * the current tail scan. Both measured ~1 ns/unit (#1669: indexing the
     * scan away cut 242M visits for 0% wall). Gate them only after those
     * scans are bounded; until then they are trend data for the report. */
    printf("    [info] tail_lookups %llu -> %llu  tail_candidates %llu -> %llu  fallback_rows "
           "%llu -> %llu\n",
           (unsigned long long)a->tail_lookups, (unsigned long long)b->tail_lookups,
           (unsigned long long)a->tail_candidates, (unsigned long long)b->tail_candidates,
           (unsigned long long)a->fallback_rows, (unsigned long long)b->fallback_rows);
    PASS();
}

static CxMetrics g_cx_big_base;
static CxMetrics g_cx_big_doubled;
static bool g_cx_big_measured = false;

static int cx_measure_bigpkg_pair(void) {
    if (g_cx_big_measured) {
        return 0;
    }
    const char *tmp = cbm_tmpdir();
    char ra[512];
    char rb[512];
    snprintf(ra, sizeof(ra), "%s/cbm_cxbig_a_XXXXXX", tmp);
    snprintf(rb, sizeof(rb), "%s/cbm_cxbig_b_XXXXXX", tmp);
    if (!cbm_mkdtemp(ra) || !cbm_mkdtemp(rb)) {
        return -1;
    }
    if (cx_build_bigpkg(ra, CX_K_BASE) != 0 || cx_build_bigpkg(rb, CX_K_BASE * 2) != 0) {
        return -1;
    }
    char db1[600];
    char db2[600];
    snprintf(db1, sizeof(db1), "%s/cx.db", ra);
    snprintf(db2, sizeof(db2), "%s/cx.db", rb);
    if (cx_run(ra, db1, &g_cx_big_base) != 0) {
        return -1;
    }
    if (cx_run(rb, db2, &g_cx_big_doubled) != 0) {
        return -1;
    }
    g_cx_big_measured = true;
    return 0;
}

/* One growing package instead of independent modules. Nodes and edges must
 * still be linear in file count — and so must Σ per-file registry work: a
 * build scoped to the file's MODULE or NAMESPACE pays package-size per file
 * and lands at ratio ~4 here. Only a per-FILE-scoped build stays at ~2. This
 * is the exact #1669 growth pattern (per-file work tracking corpus share). */
TEST(complexity_shared_package_growth_stays_linear) {
    if (cx_measure_bigpkg_pair() != 0) {
        FAIL("failed to build/run the big-package corpus pair");
    }
    const CxMetrics *a = &g_cx_big_base;
    const CxMetrics *b = &g_cx_big_doubled;

    double node_r = cx_ratio(b->nodes, a->nodes);
    double edge_r = cx_ratio(b->edges, a->edges);
    printf("    nodes %d -> %d (ratio %.2f)  edges %d -> %d (ratio %.2f)\n", a->nodes, b->nodes,
           node_r, a->edges, b->edges, edge_r);
    ASSERT_GT(a->nodes, 30);
    ASSERT_TRUE(node_r >= CX_RATIO_LO && node_r <= CX_RATIO_HI);
    ASSERT_TRUE(edge_r >= CX_RATIO_LO && edge_r <= CX_RATIO_HI);

    printf("    perfile_defs %llu -> %llu (ratio %.2f; linear ~2, namespace/module-scoped ~4)\n",
           (unsigned long long)a->perfile_defs, (unsigned long long)b->perfile_defs,
           cx_ratio((double)b->perfile_defs, (double)a->perfile_defs));
    /* Non-vacuous floor (false-guard audit): the package produces real
     * registry work; zero means the counter wiring broke. */
    ASSERT_GT((long long)a->perfile_defs, (long long)CX_MIN_BASE_WORK);
    double defs_r = cx_ratio((double)b->perfile_defs, (double)a->perfile_defs);
    ASSERT_TRUE(defs_r <= CX_RATIO_HI);
    PASS();
}

/* Throughput report — information only, never a gate (CI-determinism rule:
 * rates depend on the machine and scheduler, so a threshold would be a
 * lottery). Written locally under private/ (gitignored); CBM_COMPLEXITY_
 * REPORT_DIR overrides. Skipped on starved legs where rates are meaningless. */
TEST(complexity_throughput_report_written) {
    const char *skip_perf = getenv("CBM_SKIP_PERF");
    if (skip_perf && skip_perf[0] == '1') {
        /* Deliberate operator config, not a hidden environment failure
         * (no-skips policy): rates measured under CBM_SKIP_PERF starvation
         * would only mislead, so reporting is OFF and there is nothing left
         * for this test to assert. */
        fprintf(stderr, "  [complexity] CBM_SKIP_PERF=1: throughput report disabled by config\n");
        PASS();
    }
    if (cx_measure_pair() != 0) {
        FAIL("failed to build/run the complexity corpus pair");
    }
    const char *dir = getenv("CBM_COMPLEXITY_REPORT_DIR");
    if (!dir || !dir[0]) {
        dir = "private/benchmarks";
    }
    if (th_mkdir_p(dir) != 0) {
        FAIL("report dir not creatable (set CBM_COMPLEXITY_REPORT_DIR to a writable path)");
    }
    char path[1024];
    snprintf(path, sizeof(path), "%s/complexity-%lld.json", dir, (long long)time(NULL));
    FILE *f = fopen(path, "w");
    ASSERT_NOT_NULL(f);

    const CxMetrics *a = &g_cx_base;
    const CxMetrics *b = &g_cx_doubled;
#if defined(__APPLE__)
    const char *plat = "darwin";
#elif defined(_WIN32)
    const char *plat = "windows";
#else
    const char *plat = "linux";
#endif
#if defined(__aarch64__) || defined(_M_ARM64)
    const char *arch = "arm64";
#else
    const char *arch = "x86_64";
#endif
    fprintf(f, "{\n  \"schema\": 1,\n  \"suite\": \"complexity\",\n");
    fprintf(f, "  \"timestamp\": %lld,\n  \"platform\": \"%s\",\n  \"arch\": \"%s\",\n",
            (long long)time(NULL), plat, arch);
    fprintf(f, "  \"k_base\": %d,\n  \"files_per_module\": %d,\n", CX_K_BASE, CX_FILES_PER_MOD);
    fprintf(f, "  \"runs\": [\n");
    const CxMetrics *runs[2] = {a, b};
    for (int i = 0; i < 2; i++) {
        const CxMetrics *m = runs[i];
        fprintf(f,
                "    {\"k\": %d, \"nodes\": %d, \"edges\": %d, \"wall_s\": %.3f,\n"
                "     \"nodes_per_s\": %.0f, \"edges_per_s\": %.0f,\n"
                "     \"perfile_defs\": %llu, \"tail_candidates\": %llu, \"fallback_rows\": "
                "%llu}%s\n",
                i == 0 ? CX_K_BASE : CX_K_BASE * 2, m->nodes, m->edges, m->wall_s,
                m->wall_s > 0 ? (double)m->nodes / m->wall_s : 0.0,
                m->wall_s > 0 ? (double)m->edges / m->wall_s : 0.0,
                (unsigned long long)m->perfile_defs, (unsigned long long)m->tail_candidates,
                (unsigned long long)m->fallback_rows, i == 0 ? "," : "");
    }
    fprintf(f, "  ],\n");
    fprintf(f, "  \"languages\": [\n");
    for (int t = 0; t < CX_TEMPLATE_COUNT; t++) {
        fprintf(f,
                "    {\"name\": \"%s\", \"nodes\": [%d, %d], \"edges\": [%d, %d], "
                "\"node_ratio\": %.3f}%s\n",
                CX_TEMPLATES[t].dirname, a->lang_nodes[t], b->lang_nodes[t], a->lang_edges[t],
                b->lang_edges[t], cx_ratio(b->lang_nodes[t], a->lang_nodes[t]),
                t + 1 < CX_TEMPLATE_COUNT ? "," : "");
    }
    fprintf(f, "  ],\n");
    fprintf(f, "  \"passes_ms\": {\n");
    for (int i = 0; i < 2; i++) {
        const CxMetrics *m = runs[i];
        fprintf(f, "    \"k%d\": {", i == 0 ? CX_K_BASE : CX_K_BASE * 2);
        for (int j = 0; j < m->pass_count; j++) {
            fprintf(f, "%s\"%s\": %ld", j == 0 ? "" : ", ", m->passes[j].name, m->passes[j].ms);
        }
        fprintf(f, "}%s\n", i == 0 ? "," : "");
    }
    fprintf(f, "  },\n");
    fprintf(f, "  \"ratios\": {\"nodes\": %.3f, \"edges\": %.3f, \"perfile_defs\": %.3f},\n",
            cx_ratio(b->nodes, a->nodes), cx_ratio(b->edges, a->edges),
            cx_ratio((double)b->perfile_defs, (double)a->perfile_defs));
    /* Languages without a provider, so the coverage boundary is explicit in
     * the artifact rather than implied. */
    fprintf(f, "  \"skipped_languages\": [");
    bool first = true;
    for (int lang = 0; lang < CBM_LANG_COUNT; lang++) {
        bool covered = false;
        for (int t = 0; t < CX_TEMPLATE_COUNT; t++) {
            if (CX_TEMPLATES[t].lang == (CBMLanguage)lang) {
                covered = true;
            }
        }
        char fixdir[512];
        if (!covered && cx_fixture_dir_for((CBMLanguage)lang, fixdir, sizeof(fixdir))) {
            covered = true;
        }
        if (!covered) {
            const char *name = cbm_language_name((CBMLanguage)lang);
            if (name && name[0]) {
                fprintf(f, "%s\"%s\"", first ? "" : ", ", name);
                first = false;
            }
        }
    }
    fprintf(f, "]\n}\n");
    fclose(f);
    printf("    report: %s\n", path);
    PASS();
}

SUITE(complexity) {
    RUN_TEST(complexity_replicated_modules_scale_linearly);
    RUN_TEST(complexity_perfile_registry_work_is_linear);
    RUN_TEST(complexity_shared_package_growth_stays_linear);
    RUN_TEST(complexity_throughput_report_written);
}