manifest: explicit Constraints + conflict-detection + Default-driven init

Step 3 of the bottom-up plan. Three issues in one commit because the
changes interlock on OctadConfig's shape and DatabaseConfig's
effective_backend signature.

V-L2-D1 — explicit `enable_constraints`:
  Constraints was a first-class concern in ADR-0001 but was treated
  in code as "implied when count > 2". Promoted to an explicit
  OctadConfig field with serde default = true. The "+ 1 if count > 2"
  arithmetic in enabled_count is gone; the new implementation is a
  straight popcount over the six optional toggles plus 2 inherent
  dimensions. print_status reads enable_constraints directly.
  Two new unit tests assert the count is bounded by 2..=8 across
  all 64 toggle combinations and that the arithmetic is exact.

V-L2-E1 — refuse conflicting backend/target_db:
  effective_backend was value-based: `backend != "postgresql"` was
  used as a proxy for "user-set", which silently picked sqlite when
  a user explicitly set `backend = "postgresql"` alongside a legacy
  `target-db = "sqlite"`. Replaced with a fall-through match that
  errors loudly on conflict and returns `Ok(default)` otherwise.
  Signature is now `Result<&str>`; callers in main.rs + print_status
  propagate. Four new unit tests cover each branch (conflict,
  agreement, modern-only, legacy-only, default).

V-L2-O1 — init_manifest reads Default + adds --force/--name:
  Template values are now derived from OctadConfig::default() rather
  than hardcoded strings, so flipping a default in code automatically
  flows into the generated file. Added --force (overwrite existing)
  and --name (override project name) flags to `verisimiser init`.
  A regression test asserts the OctadConfig::default() invariant the
  template depends on.

Test fixtures in codegen/{overlay,query}.rs and the integration test
add the new enable_constraints field. tests/integration_test.rs's
backward-compat case calls .effective_backend().unwrap() for the
new Result signature.

Verified locally:
- cargo fmt --all -- --check clean
- cargo clippy --all-targets -- -D warnings clean
- cargo test reports 42 lib + 9 integration = 51 tests, 0 failed
  (was 35 + 9 = 44; +7 manifest unit tests)

Closes #34, #35, #36

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath

src/codegen/overlay.rs

@@ -289,6 +289,7 @@ mod tests {
             enable_lineage: true,
             enable_temporal: true,
             enable_access_control: true,
+            enable_constraints: true,
             enable_simulation: true,
         };
         let ddl = generate_sidecar_schema(&schema, &octad);
@@ -309,6 +310,7 @@ mod tests {
             enable_lineage: false,
             enable_temporal: false,
             enable_access_control: false,
+            enable_constraints: false,
             enable_simulation: false,
         };
         let ddl = generate_sidecar_schema(&schema, &octad);

src/codegen/query.rs

@@ -343,6 +343,7 @@ mod tests {
             enable_lineage: true,
             enable_temporal: true,
             enable_access_control: true,
+            enable_constraints: true,
             enable_simulation: false,
         };
         let interceptors = generate_interceptors(&schema, &octad, DatabaseBackend::SQLite);
@@ -364,6 +365,7 @@ mod tests {
             enable_lineage: false,
             enable_temporal: false,
             enable_access_control: false,
+            enable_constraints: false,
             enable_simulation: false,
         };
         let interceptors = generate_interceptors(&schema, &octad, DatabaseBackend::SQLite);
@@ -384,11 +386,15 @@ mod tests {
             enable_lineage: false,
             enable_temporal: false,
             enable_access_control: false,
+            enable_constraints: false,
             enable_simulation: false,
         };
         let interceptors = generate_interceptors(&schema, &octad, DatabaseBackend::SQLite);
 
-        let view = interceptors[0].provenance_view.as_ref().expect("TODO: handle error");
+        let view = interceptors[0]
+            .provenance_view
+            .as_ref()
+            .expect("TODO: handle error");
         assert!(view.contains("verisimdb_posts_with_provenance"));
         assert!(view.contains("posts.id"));
         assert!(view.contains("posts.title"));
@@ -403,11 +409,15 @@ mod tests {
             enable_lineage: false,
             enable_temporal: true,
             enable_access_control: false,
+            enable_constraints: false,
             enable_simulation: false,
         };
         let interceptors = generate_interceptors(&schema, &octad, DatabaseBackend::SQLite);
 
-        let view = interceptors[0].temporal_view.as_ref().expect("TODO: handle error");
+        let view = interceptors[0]
+            .temporal_view
+            .as_ref()
+            .expect("TODO: handle error");
         assert!(view.contains("verisimdb_posts_with_temporal"));
         assert!(view.contains("verisimdb_temporal_versions"));
         assert!(view.contains("valid_to IS NULL"));

src/main.rs

@@ -34,6 +34,12 @@ enum Commands {
         /// Database backend: postgresql, sqlite, or mongodb.
         #[arg(short, long, default_value = "postgresql")]
         database: String,
+        /// Project name (default: "my-augmented-db").
+        #[arg(short, long)]
+        name: Option<String>,
+        /// Overwrite an existing verisimiser.toml.
+        #[arg(short, long)]
+        force: bool,
     },
     /// Parse the target database schema and generate sidecar overlay + interceptors.
     Generate {
@@ -86,7 +92,11 @@ enum Commands {
 fn main() -> Result<()> {
     let cli = Cli::parse();
     match cli.command {
-        Commands::Init { database } => manifest::init_manifest(&database),
+        Commands::Init {
+            database,
+            name,
+            force,
+        } => manifest::init_manifest(&database, name.as_deref(), force),
 
         Commands::Generate { manifest, output } => {
             let m = manifest::load_manifest(&manifest)?;
@@ -104,7 +114,7 @@ fn main() -> Result<()> {
             };
 
             // Determine the backend for SQL dialect selection.
-            let backend_name = m.database.effective_backend();
+            let backend_name = m.database.effective_backend()?;
             let backend = abi::DatabaseBackend::from_str(backend_name)
                 .unwrap_or(abi::DatabaseBackend::PostgreSQL);
 
@@ -139,7 +149,7 @@ fn main() -> Result<()> {
             } else {
                 &m.verisimiser.name
             };
-            let backend = m.database.effective_backend();
+            let backend = m.database.effective_backend()?;
             println!(
                 "Starting VeriSimiser augmentation for {} ({})",
                 name, backend
@@ -183,8 +193,7 @@ fn main() -> Result<()> {
 
         Commands::Status { manifest } => {
             let m = manifest::load_manifest(&manifest)?;
-            manifest::print_status(&m);
-            Ok(())
+            manifest::print_status(&m)
         }
 
         Commands::Octad => {