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.

docs/modules/signals/evidence/README.md

@@ -2,46 +2,82 @@
 
 Artifacts prepared 2025-12-01 (UTC) for DSSE signing and Evidence Locker ingest:
 
-- Decay config: `docs/modules/signals/decay/confidence_decay_config.yaml`
-- Unknowns scoring manifest: `docs/modules/signals/unknowns/unknowns_scoring_manifest.json`
-- Heuristic catalog + schema + fixtures: `docs/modules/signals/heuristics/`
-- Checksums: `docs/modules/signals/SHA256SUMS`
+| Artifact | Path | Predicate |
+|----------|------|-----------|
+| Decay config | `docs/modules/signals/decay/confidence_decay_config.yaml` | `stella.ops/confidenceDecayConfig@v1` |
+| Unknowns manifest | `docs/modules/signals/unknowns/unknowns_scoring_manifest.json` | `stella.ops/unknownsScoringManifest@v1` |
+| Heuristics catalog | `docs/modules/signals/heuristics/heuristics.catalog.json` | `stella.ops/heuristicCatalog@v1` |
+| Checksums | `docs/modules/signals/SHA256SUMS` | — |
 
-Planned Evidence Locker paths (to fill post-signing):
-- `evidence-locker/signals/decay/2025-12-01/confidence_decay_config.dsse`
-- `evidence-locker/signals/unknowns/2025-12-01/unknowns_scoring_manifest.dsse`
-- `evidence-locker/signals/heuristics/2025-12-01/heuristics_catalog.dsse`
-- `evidence-locker/signals/heuristics/2025-12-01/fixtures/` (golden inputs/outputs)
+## CI Automated Signing
 
-Pending steps:
-0) Provide signing key: CI/ops should supply `COSIGN_PRIVATE_KEY_B64` (base64 of private key) and optional `COSIGN_PASSWORD`. Local dev can place a key at `tools/cosign/cosign.key` (see `tools/cosign/cosign.key.example` stub) or decode the env var to `/tmp/cosign.key`. The helper script `tools/cosign/sign-signals.sh` auto-detects the key and cosign version.
-1) Sign each artifact with its predicate (cosign v3.0.2 in `/usr/local/bin`, use `--bundle`; v2.6.0 fallback in `tools/cosign` also works with `--output-signature`):
-   - `stella.ops/confidenceDecayConfig@v1`
-   - `stella.ops/unknownsScoringManifest@v1`
-   - `stella.ops/heuristicCatalog@v1`
-   Shortcut: `OUT_DIR=evidence-locker/signals/2025-12-01 tools/cosign/sign-signals.sh`
-   Example (v3, replace KEY):
-   ```bash
-   cosign sign-blob \
-     --key cosign.key \
-     --predicate-type stella.ops/confidenceDecayConfig@v1 \
-     --bundle confidence_decay_config.sigstore.json \
-     decay/confidence_decay_config.yaml
-   ```
-   v2.6.0 fallback (if PATH prefixed with `tools/cosign`):
-   ```bash
-   cosign sign-blob \
-     --key cosign.key \
-     --predicate-type stella.ops/confidenceDecayConfig@v1 \
-     --output-signature confidence_decay_config.dsse \
-     decay/confidence_decay_config.yaml
-   ```
-2) Record SHA256 from `SHA256SUMS` in DSSE annotations (or bundle metadata); keep canonical filenames:
-   - v3: `confidence_decay_config.sigstore.json`, `unknowns_scoring_manifest.sigstore.json`, `heuristics_catalog.sigstore.json`
-   - v2 fallback: `.dsse` signatures.
-3) Place signed envelopes + checksums in the Evidence Locker paths above; update sprint tracker Delivery Tracker rows 5–7 and Decisions & Risks with the final URIs.
-4) Add signer/approver IDs to the sprint Execution Log once signatures are complete.
+The `.gitea/workflows/signals-dsse-sign.yml` workflow automates DSSE signing.
 
-Notes:
-- Use UTC timestamps in DSSE `issuedAt`.
-- Ensure offline parity by copying envelopes + SHA256SUMS into the offline kit bundle when ready.
+### Prerequisites (CI Secrets)
+| Secret | Description |
+|--------|-------------|
+| `COSIGN_PRIVATE_KEY_B64` | Base64-encoded cosign private key (required for production) |
+| `COSIGN_PASSWORD` | Password for encrypted key (if applicable) |
+| `CI_EVIDENCE_LOCKER_TOKEN` | Token for Evidence Locker push (optional) |
+
+### Trigger
+- **Automatic**: Push to `main` affecting `docs/modules/signals/**` or `tools/cosign/sign-signals.sh`
+- **Manual**: Workflow dispatch with `allow_dev_key=1` for testing
+
+### Output
+Signed artifacts uploaded as workflow artifact `signals-dsse-signed-{run}` and optionally pushed to Evidence Locker.
+
+## Development Signing (Local Testing)
+
+A development key pair is available for smoke tests:
+
+```bash
+# Sign 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 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
+```
+
+**Note**: Dev key signatures are NOT suitable for Evidence Locker or production use.
+
+## Production Signing (Manual)
+
+For production signing without CI:
+
+```bash
+# Option 1: Place key file
+cp /path/to/production.key tools/cosign/cosign.key
+OUT_DIR=evidence-locker/signals/2025-12-01 tools/cosign/sign-signals.sh
+
+# Option 2: Use base64 env var
+export COSIGN_PRIVATE_KEY_B64=$(cat production.key | base64 -w0)
+export COSIGN_PASSWORD=your-password
+OUT_DIR=evidence-locker/signals/2025-12-01 tools/cosign/sign-signals.sh
+```
+
+## Evidence Locker Paths
+
+Post-signing, artifacts go to:
+- `evidence-locker/signals/2025-12-01/confidence_decay_config.sigstore.json`
+- `evidence-locker/signals/2025-12-01/unknowns_scoring_manifest.sigstore.json`
+- `evidence-locker/signals/2025-12-01/heuristics_catalog.sigstore.json`
+- `evidence-locker/signals/2025-12-01/SHA256SUMS`
+
+## Post-Signing Checklist
+
+1. Verify signatures against public key
+2. Update sprint tracker (SPRINT_0140) Delivery Tracker rows 5–7
+3. Add signer ID to Execution Log
+4. Copy to offline kit bundle for air-gap parity
+
+## Notes
+
+- All timestamps use UTC ISO-8601 format
+- Signatures disable tlog upload (`--tlog-upload=false`) for offline compatibility
+- See `tools/cosign/README.md` for detailed key management and CI setup