feat(sca): runtime SCA reachability (#17156)

## Description

Implements **Runtime SCA Reachability** — the tracer reports which vulnerable symbols (functions/methods in third-party libraries with known CVEs) have actually been invoked at runtime, reducing false positives from static SCA analysis.

**RFC**: https://docs.google.com/document/d/1xDw9iG6h41VCEgJGTqoJdruRaNS4pYgNifO6nhiizWA/edit?tab=t.a9gurws0d8ua

### How it works

When `DD_APPSEC_SCA_ENABLED=true`:

1. **CVE data loading** — At tracer startup, reads `_cve_data.json` containing vulnerability targets (symbol + CVE + version constraint). Filters against installed packages.
2. **Runtime instrumentation** — For each applicable CVE target, applies bytecode injection (`inject_hook`) to the vulnerable function. Supports both eager (already-imported modules) and lazy (via `ModuleWatchdog` for deferred imports).
3. **CVE registration** — Immediately registers all applicable CVEs on their dependencies with `reached: []` in the telemetry `app-dependencies-loaded` payload. The backend knows which CVEs apply before any symbol is hit.
4. **Reachability detection** — When an instrumented function executes, the hook captures the caller's file path, method name, and line number, then attaches it to the CVE's `reached` array. Only the first occurrence is reported per CVE (RFC: "reporting a single occurrence is sufficient").
5. **Telemetry reporting** — On each heartbeat (default 60s), dependencies with new reachability data are re-reported with all their metadata via `app-dependencies-loaded`.

### Telemetry payload (RFC v3)

```json
{
  "request_type": "app-dependencies-loaded",
  "payload": {
    "dependencies": [
      {
        "name": "requests",
        "version": "2.31.0",
        "metadata": [
          {
            "type": "reachability",
            "value": "{\"id\":\"CVE-2024-35195\",\"reached\":[{\"path\":\"myapp/views.py\",\"method\":\"handle_request\",\"line\":42}]}"
          }
        ]
      }
    ]
  }
}
```

Before any symbol is hit, CVEs are reported with `"reached":[]`. When a symbol executes, the first caller info is added to the `reached` array.

## Performance

Benchmark: `scripts/perf_bench_heartbeat_cycles.py`

Measures `collect_report()` execution time per heartbeat cycle under different scenarios. The overhead is paid only in the background telemetry thread (every 60s), never in user request paths.

- **SCA OFF (main)**: baseline on `main` branch — old `update_imported_dependencies()` path, no `DependencyTracker`, no re-report scan
- **SCA OFF**: this branch with `DD_APPSEC_SCA_ENABLED=false` — new `DependencyTracker` with `metadata=None`, re-report scan skipped
- **SCA ON**: this branch with `DD_APPSEC_SCA_ENABLED=true` — new `DependencyTracker` with `metadata=[]`
- **Overhead**: `(SCA ON − SCA OFF) / SCA OFF`

### 1,000 dependencies (typical large application)

| Heartbeat Cycle | SCA OFF (main) | SCA OFF | SCA ON | Overhead |
|---|---|---|---|---|
| First heartbeat (all new) | 4.56ms | 4.63ms | 5.10ms | **+10.1%** |
| Idle (nothing to report) | 0.2us | 72.2us | 239.6us | **+231.8%** |
| CVE registration (100 CVEs, reached=[]) | 0.3us | 73.5us | 1.20ms | **+1527.5%** |
| SCA hits (100 hits on 50 deps) | 0.3us | 73.7us | 1.44ms | **+1857.1%** |

### 10,000 dependencies (extreme scale)

| Heartbeat Cycle | SCA OFF (main) | SCA OFF | SCA ON | Overhead |
|---|---|---|---|---|
| First heartbeat (all new) | 53.15ms | 57.18ms | 62.12ms | **+8.6%** |
| Idle (nothing to report) | 0.3us | 742.6us | 2.20ms | **+195.7%** |
| CVE registration (1,000 CVEs, reached=[]) | 0.3us | 720.7us | 13.51ms | **+1774.4%** |
| SCA hits (1,000 hits on 500 deps) | 0.3us | 718.9us | 15.56ms | **+2064.2%** |

### Payload size

| Scenario (1,000 deps) | Entries | Size |
|---|---|---|
| First heartbeat SCA OFF | 1,000 | 62 KB |
| First heartbeat SCA ON | 1,000 | 62 KB |
| CVE registration (100 CVEs) | 50 | 10 KB |
| SCA hits (100 hits) | 50 | 16 KB |

### Memory overhead

| Scenario (1,000 deps) | SCA OFF | SCA ON | Delta |
|---|---|---|---|
| Idle heartbeat | 155.3 KB | 192.5 KB | +37.2 KB |
| CVE registration (100 CVEs) | 136.4 KB | 205.8 KB | +69.4 KB |
| SCA hits (100 hits) | 136.2 KB | 208.5 KB | +72.3 KB |

> **Note on overhead**: The percentage overhead for idle, CVE registration, and SCA hits appears very high because the SCA OFF baseline includes mock/benchmark harness overhead (~72us at 1K deps) that dominates the measurement. In absolute terms:
>
> - **First heartbeat**: nearly identical across all three columns (4.56ms → 4.63ms → 5.10ms at 1K deps), confirming the `DependencyTracker` refactor adds **minimal overhead** to initial dependency discovery.
> - **Idle heartbeat with SCA OFF**: ~72us includes benchmark mock overhead; measured independently at ~8us (lock acquisition + `get_newly_imported_modules()` + lazy config check). The re-report scan is **completely skipped** when SCA is disabled.
> - **SCA ON worst case** at 1,000 dependencies: **1.44ms per 60s heartbeat** — 0.002% of the cycle.
> - **SCA ON worst case** at 10,000 dependencies with 1,000 CVEs: **16ms** — 0.027% of the heartbeat interval.
>
> All overhead runs entirely in the background telemetry thread and does not affect user request latency.

### SLO benchmark

A CI-integrated benchmark suite is available at `benchmarks/telemetry_dependencies/` with 8 scenarios covering first/idle/cve/hits phases at 100 and 1,000 dependencies. It is triggered automatically when `ddtrace/internal/telemetry/dependency*.py` or `ddtrace/appsec/sca/*` files change and compares performance between the base branch and this PR.

## Risks

- **Bytecode injection**: Uses the existing `inject_hook` infrastructure from dd-trace-py. The hook is exception-safe (wrapped in try/except) and never raises in user code.
- **Memory**: `DependencyEntry` objects add ~150 bytes per dependency vs plain strings. At 1,000 deps this is ~150KB total — negligible.
- **Lock contention**: The `DependencyTracker._lock` is held briefly during `attach_metadata` calls from the SCA hook. After the first hit per CVE (max reached=1), subsequent hook invocations short-circuit before any lock acquisition.

## Additional Notes

- Merge this PR first: DataDog/datadog-lambda-python#761
- Previous model PR benchmarks: #17092
- The static CVE JSON (`_cve_data.json`) will be replaced by Remote Config in the long-term solution

Co-authored-by: alberto.vara <alberto.vara@datadoghq.com>

Author: avara1986

.gitlab/benchmarks/bp-runner.microbenchmarks.fail-on-breach.template.yml

@@ -791,7 +791,7 @@ experiments:
               - max_rss_usage < 46.00 MB
           - name: packagesupdateimporteddependencies-import_one_stdlib
             thresholds:
-              - execution_time < 0.02 ms
+              - execution_time < 0.03 ms
               - max_rss_usage < 46.00 MB
           - name: packagesupdateimporteddependencies-import_one_stdlib_cache
             thresholds:
@@ -1076,7 +1076,7 @@ experiments:
               - max_rss_usage < 33 MB
           - name: forktime-configured
             thresholds:
-              - execution_time < 13 ms
+              - execution_time < 17 ms
               - max_rss_usage < 60 MB
 
           # rand

.riot/requirements/1428c37.txt .riot/requirements/11335dd.txt.riot/requirements/1428c37.txt renamed to .riot/requirements/11335dd.txt

@@ -2,16 +2,20 @@
 # This file is autogenerated by pip-compile with Python 3.14
 # by the following command:
 #
-#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1428c37.in
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/11335dd.in
 #
 attrs==26.1.0
 babel==2.18.0
 blinker==1.9.0
-click==8.3.1
+certifi==2026.2.25
+charset-normalizer==3.4.7
+click==8.3.2
 coverage[toml]==7.13.5
 flask==2.3.3
 flask-babel==4.0.0
+greenlet==3.4.0
 hypothesis==6.45.0
+idna==3.11
 iniconfig==2.3.0
 itsdangerous==2.2.0
 jinja2==3.1.6
@@ -21,13 +25,15 @@ opentracing==2.4.0
 packaging==26.0
 pluggy==1.6.0
 psycopg2-binary==2.9.11
-pygments==2.19.2
-pytest==9.0.2
+pygments==2.20.0
+pytest==9.0.3
 pytest-cov==7.1.0
 pytest-mock==3.15.1
 pytest-randomly==4.0.1
 pytz==2026.1.post1
+requests==2.33.1
 sortedcontainers==2.4.0
-sqlalchemy==2.0.48
+sqlalchemy==2.0.49
 typing-extensions==4.15.0
-werkzeug==3.1.7
+urllib3==2.6.3
+werkzeug==3.1.8

.riot/requirements/1df8e9a.txt .riot/requirements/148c37a.txt.riot/requirements/1df8e9a.txt renamed to .riot/requirements/148c37a.txt

@@ -2,16 +2,20 @@
 # This file is autogenerated by pip-compile with Python 3.12
 # by the following command:
 #
-#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1df8e9a.in
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/148c37a.in
 #
 attrs==26.1.0
 babel==2.18.0
 blinker==1.9.0
-click==8.3.1
+certifi==2026.2.25
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 coverage[toml]==7.13.5
 flask==3.1.3
 flask-babel==4.0.0
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 hypothesis==6.45.0
+idna==3.11
 iniconfig==2.3.0
 itsdangerous==2.2.0
 jinja2==3.1.6
@@ -21,13 +25,15 @@ opentracing==2.4.0
 packaging==26.0
 pluggy==1.6.0
 psycopg2-binary==2.9.11
-pygments==2.19.2
-pytest==9.0.2
+pygments==2.20.0
+pytest==9.0.3
 pytest-cov==7.1.0
 pytest-mock==3.15.1
 pytest-randomly==4.0.1
 pytz==2026.1.post1
+requests==2.33.1
 sortedcontainers==2.4.0
-sqlalchemy==2.0.48
+sqlalchemy==2.0.49
 typing-extensions==4.15.0
-werkzeug==3.1.7
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.riot/requirements/5cef9f9.txt .riot/requirements/176aab2.txt.riot/requirements/5cef9f9.txt renamed to .riot/requirements/176aab2.txt

@@ -2,17 +2,21 @@
 # This file is autogenerated by pip-compile with Python 3.9
 # by the following command:
 #
-#    pip-compile --allow-unsafe --no-annotate .riot/requirements/5cef9f9.in
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/176aab2.in
 #
 attrs==26.1.0
 babel==2.18.0
 blinker==1.9.0
+certifi==2026.2.25
+charset-normalizer==3.4.7
 click==8.1.8
 coverage[toml]==7.10.7
 exceptiongroup==1.3.1
 flask==2.3.3
 flask-babel==4.0.0
+greenlet==3.2.5
 hypothesis==6.45.0
+idna==3.11
 importlib-metadata==8.7.1
 iniconfig==2.1.0
 itsdangerous==2.2.0
@@ -23,15 +27,17 @@ opentracing==2.4.0
 packaging==26.0
 pluggy==1.6.0
 psycopg2-binary==2.9.11
-pygments==2.19.2
+pygments==2.20.0
 pytest==8.4.2
 pytest-cov==7.1.0
 pytest-mock==3.15.1
 pytest-randomly==4.0.1
 pytz==2026.1.post1
+requests==2.32.5
 sortedcontainers==2.4.0
-sqlalchemy==2.0.48
+sqlalchemy==2.0.49
 tomli==2.4.1
 typing-extensions==4.15.0
-werkzeug==3.1.7
+urllib3==2.6.3
+werkzeug==3.1.8
 zipp==3.23.0

.riot/requirements/6843c56.txt .riot/requirements/18269eb.txt.riot/requirements/6843c56.txt renamed to .riot/requirements/18269eb.txt

@@ -2,16 +2,20 @@
 # This file is autogenerated by pip-compile with Python 3.13
 # by the following command:
 #
-#    pip-compile --allow-unsafe --no-annotate .riot/requirements/6843c56.in
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/18269eb.in
 #
 attrs==26.1.0
 babel==2.18.0
 blinker==1.9.0
-click==8.3.1
+certifi==2026.2.25
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 coverage[toml]==7.13.5
 flask==3.1.3
 flask-babel==4.0.0
+greenlet==3.4.0
 hypothesis==6.45.0
+idna==3.11
 iniconfig==2.3.0
 itsdangerous==2.2.0
 jinja2==3.1.6
@@ -21,13 +25,15 @@ opentracing==2.4.0
 packaging==26.0
 pluggy==1.6.0
 psycopg2-binary==2.9.11
-pygments==2.19.2
-pytest==9.0.2
+pygments==2.20.0
+pytest==9.0.3
 pytest-cov==7.1.0
 pytest-mock==3.15.1
 pytest-randomly==4.0.1
 pytz==2026.1.post1
+requests==2.33.1
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-sqlalchemy==2.0.48
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 typing-extensions==4.15.0
-werkzeug==3.1.7
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.riot/requirements/1335c92.txt .riot/requirements/190e5df.txt.riot/requirements/1335c92.txt renamed to .riot/requirements/190e5df.txt

@@ -2,17 +2,21 @@
 # This file is autogenerated by pip-compile with Python 3.10
 # by the following command:
 #
-#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1335c92.in
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/190e5df.in
 #
 attrs==26.1.0
 babel==2.18.0
 blinker==1.9.0
-click==8.3.1
+certifi==2026.2.25
+charset-normalizer==3.4.7
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 coverage[toml]==7.13.5
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 hypothesis==6.45.0
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 iniconfig==2.3.0
 itsdangerous==2.2.0
 jinja2==3.1.6
@@ -22,14 +26,16 @@ opentracing==2.4.0
 packaging==26.0
 pluggy==1.6.0
 psycopg2-binary==2.9.11
-pygments==2.19.2
-pytest==9.0.2
+pygments==2.20.0
+pytest==9.0.3
 pytest-cov==7.1.0
 pytest-mock==3.15.1
 pytest-randomly==4.0.1
 pytz==2026.1.post1
+requests==2.33.1
 sortedcontainers==2.4.0
-sqlalchemy==2.0.48
+sqlalchemy==2.0.49
 tomli==2.4.1
 typing-extensions==4.15.0
-werkzeug==3.1.7
+urllib3==2.6.3
+werkzeug==3.1.8

.riot/requirements/1ab3731.txt

@@ -0,0 +1,19 @@
+#
+# This file is autogenerated by pip-compile with Python 3.12
+# by the following command:
+#
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1ab3731.in
+#
+attrs==26.1.0
+coverage[toml]==7.13.5
+hypothesis==6.45.0
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+pytest==9.0.3
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+pytest-mock==3.15.1
+sortedcontainers==2.4.0

.riot/requirements/1d488a9.txt

@@ -0,0 +1,19 @@
+#
+# This file is autogenerated by pip-compile with Python 3.13
+# by the following command:
+#
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1d488a9.in
+#
+attrs==26.1.0
+coverage[toml]==7.13.5
+hypothesis==6.45.0
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+sortedcontainers==2.4.0

.riot/requirements/1f1aeb9.txt .riot/requirements/1dbdbea.txt.riot/requirements/1f1aeb9.txt renamed to .riot/requirements/1dbdbea.txt

@@ -2,16 +2,20 @@
 # This file is autogenerated by pip-compile with Python 3.12
 # by the following command:
 #
-#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1f1aeb9.in
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1dbdbea.in
 #
 attrs==26.1.0
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-click==8.3.1
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 coverage[toml]==7.13.5
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 hypothesis==6.45.0
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 iniconfig==2.3.0
 itsdangerous==2.2.0
 jinja2==3.1.6
@@ -21,13 +25,15 @@ opentracing==2.4.0
 packaging==26.0
 pluggy==1.6.0
 psycopg2-binary==2.9.11
-pygments==2.19.2
-pytest==9.0.2
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 typing-extensions==4.15.0
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+urllib3==2.6.3
+werkzeug==3.1.8

.riot/requirements/1e5dd1a.txt

@@ -0,0 +1,22 @@
+#
+# This file is autogenerated by pip-compile with Python 3.10
+# by the following command:
+#
+#    pip-compile --allow-unsafe --no-annotate .riot/requirements/1e5dd1a.in
+#
+attrs==26.1.0
+coverage[toml]==7.13.5
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