Add signal contracts for reachability, exploitability, trust, and unknown symbols

- Introduced `ReachabilityState`, `RuntimeHit`, `ExploitabilitySignal`, `ReachabilitySignal`, `SignalEnvelope`, `SignalType`, `TrustSignal`, and `UnknownSymbolSignal` records to define various signal types and their properties.
- Implemented JSON serialization attributes for proper data interchange.
- Created project files for the new signal contracts library and corresponding test projects.
- Added deterministic test fixtures for micro-interaction testing.
- Included cryptographic keys for secure operations with cosign.

tools/cosign/README.md

@@ -16,12 +16,93 @@
 - v3 verify: `cosign verify-blob --bundle confidence_decay_config.sigstore.json decay/confidence_decay_config.yaml`
 - To force offline fallback, export `PATH=./tools/cosign:$PATH` (ensures v2.6.0 is used).
 
-## CI / secrets
+## CI Workflow: signals-dsse-sign.yml
+
+The `.gitea/workflows/signals-dsse-sign.yml` workflow automates DSSE signing for Signals artifacts.
+
+### Required Secrets
+| Secret | Description | Required |
+|--------|-------------|----------|
+| `COSIGN_PRIVATE_KEY_B64` | Base64-encoded cosign private key | Yes (for production) |
+| `COSIGN_PASSWORD` | Password for the private key | If key is encrypted |
+| `CI_EVIDENCE_LOCKER_TOKEN` | Token for Evidence Locker upload | Optional |
+
+### Trigger Options
+1. **Automatic**: On push to `main` when signals artifacts change
+2. **Manual**: Via workflow_dispatch with options:
+   - `out_dir`: Output directory (default: `evidence-locker/signals/2025-12-01`)
+   - `allow_dev_key`: Set to `1` for testing with dev key
+
+### Setting Up CI Secrets
+```bash
+# Generate production key pair (do this once, securely)
+cosign generate-key-pair
+
+# Base64 encode the private key
+cat cosign.key | base64 -w0 > cosign.key.b64
+
+# Add to Gitea secrets:
+# - COSIGN_PRIVATE_KEY_B64: contents of cosign.key.b64
+# - COSIGN_PASSWORD: password used during key generation
+```
+
+## CI / secrets (manual usage)
 - CI should provide a base64-encoded private key via secret `COSIGN_PRIVATE_KEY_B64` and optional password in `COSIGN_PASSWORD`.
 - Example bootstrap in jobs:
   ```bash
-  echo \"$COSIGN_PRIVATE_KEY_B64\" | base64 -d > /tmp/cosign.key
+  echo "$COSIGN_PRIVATE_KEY_B64" | base64 -d > /tmp/cosign.key
   chmod 600 /tmp/cosign.key
-  COSIGN_PASSWORD=\"${COSIGN_PASSWORD:-}\" cosign version
+  COSIGN_PASSWORD="${COSIGN_PASSWORD:-}" cosign version
   ```
 - For local dev, copy your own key to `tools/cosign/cosign.key` or export `COSIGN_PRIVATE_KEY_B64` before running signing scripts. Never commit real keys; only `cosign.key.example` lives in git.
+
+## Development signing key
+
+A development key pair is provided for local testing and smoke tests:
+
+| File | Description |
+|------|-------------|
+| `tools/cosign/cosign.dev.key` | Private key (password-protected) |
+| `tools/cosign/cosign.dev.pub` | Public key for verification |
+
+### Usage
+```bash
+# Sign signals artifacts with dev key
+COSIGN_ALLOW_DEV_KEY=1 COSIGN_PASSWORD=stellaops-dev \
+  OUT_DIR=docs/modules/signals/dev-test \
+  tools/cosign/sign-signals.sh
+
+# Verify a signature
+cosign verify-blob \
+  --key tools/cosign/cosign.dev.pub \
+  --bundle docs/modules/signals/dev-test/confidence_decay_config.sigstore.json \
+  docs/modules/signals/decay/confidence_decay_config.yaml
+```
+
+### Security Notes
+- Password: `stellaops-dev` (do not reuse elsewhere)
+- **NOT** for production or Evidence Locker ingestion
+- Real signing requires the Signals Guild key via `COSIGN_PRIVATE_KEY_B64` (CI) or `tools/cosign/cosign.key` (local drop-in)
+- `sign-signals.sh` requires `COSIGN_ALLOW_DEV_KEY=1` to use the dev key; otherwise it refuses
+- The signing helper disables tlog upload (`--tlog-upload=false`) and auto-accepts prompts (`--yes`) for offline runs
+
+## Signing Scripts
+
+### sign-signals.sh
+Signs decay config, unknowns manifest, and heuristics catalog with DSSE envelopes.
+
+```bash
+# Production (CI secret or cosign.key drop-in)
+OUT_DIR=evidence-locker/signals/2025-12-01 tools/cosign/sign-signals.sh
+
+# Development (dev key)
+COSIGN_ALLOW_DEV_KEY=1 COSIGN_PASSWORD=stellaops-dev \
+  OUT_DIR=docs/modules/signals/dev-test \
+  tools/cosign/sign-signals.sh
+```
+
+### Key Resolution Order
+1. `COSIGN_KEY_FILE` environment variable
+2. `COSIGN_PRIVATE_KEY_B64` (decoded to temp file)
+3. `tools/cosign/cosign.key` (production drop-in)
+4. `tools/cosign/cosign.dev.key` (only if `COSIGN_ALLOW_DEV_KEY=1`)