refactor: use project-named state file and store prompt/params directly

- State filename now derives from config: cards.bulkgen.yaml produces
  .cards.bulkgen-state.yaml instead of .bulkgen.state.yaml
- Store resolved prompt text and extra params directly in state file
  instead of hashing them, making state files human-readable
- Only file input contents remain hashed (SHA-256)
- Thread project_name through builder and CLI
- Remove hash_string() and _extra_hash() helpers
- Update .gitignore pattern to .*.bulkgen-state.yaml

bulkgen/state.py

@@ -1,4 +1,4 @@
-"""Incremental build state tracking via ``.bulkgen.state.yaml``."""
+"""Incremental build state tracking via ``.<project>.bulkgen-state.yaml``."""
 
 from __future__ import annotations
 
@@ -8,16 +8,23 @@ from pathlib import Path
 import yaml
 from pydantic import BaseModel
 
-STATE_FILENAME = ".bulkgen.state.yaml"
+
+def state_filename(project_name: str) -> str:
+    """Return the state filename for a given project name.
+
+    For a config file named ``cards.bulkgen.yaml`` the project name is
+    ``cards`` and the state file is ``.cards.bulkgen-state.yaml``.
+    """
+    return f".{project_name}.bulkgen-state.yaml"
 
 
 class TargetState(BaseModel):
     """Recorded state of a single target from its last successful build."""
 
     input_hashes: dict[str, str]
-    prompt_hash: str
+    prompt: str
     model: str
-    extra_hash: str = ""
+    extra_params: dict[str, object] = {}
 
 
 class BuildState(BaseModel):
@@ -35,14 +42,9 @@ def hash_file(path: Path) -> str:
     return h.hexdigest()
 
 
-def hash_string(value: str) -> str:
-    """Compute the SHA-256 hex digest of a string."""
-    return hashlib.sha256(value.encode("utf-8")).hexdigest()
-
-
-def load_state(project_dir: Path) -> BuildState:
+def load_state(project_dir: Path, project_name: str) -> BuildState:
     """Load build state from disk, returning empty state if the file is missing."""
-    state_path = project_dir / STATE_FILENAME
+    state_path = project_dir / state_filename(project_name)
     if not state_path.exists():
         return BuildState()
     with state_path.open() as f:
@@ -52,20 +54,13 @@ def load_state(project_dir: Path) -> BuildState:
     return BuildState.model_validate(raw)
 
 
-def save_state(state: BuildState, project_dir: Path) -> None:
+def save_state(state: BuildState, project_dir: Path, project_name: str) -> None:
     """Persist build state to disk."""
-    state_path = project_dir / STATE_FILENAME
+    state_path = project_dir / state_filename(project_name)
     with state_path.open("w") as f:
         yaml.dump(state.model_dump(), f, default_flow_style=False, sort_keys=False)
 
 
-def _extra_hash(params: dict[str, object]) -> str:
-    """Hash extra target parameters (width, height, etc.) for change detection."""
-    if not params:
-        return ""
-    return hash_string(str(sorted(params.items())))
-
-
 def is_target_dirty(
     target_name: str,
     *,
@@ -98,10 +93,10 @@ def is_target_dirty(
     if prev.model != model:
         return True
 
-    if prev.prompt_hash != hash_string(resolved_prompt):
+    if prev.prompt != resolved_prompt:
         return True
 
-    if prev.extra_hash != _extra_hash(extra_params):
+    if prev.extra_params != extra_params:
         return True
 
     for dep_path in dep_files:
@@ -131,7 +126,7 @@ def record_target_state(
 
     state.targets[target_name] = TargetState(
         input_hashes=input_hashes,
-        prompt_hash=hash_string(resolved_prompt),
+        prompt=resolved_prompt,
         model=model,
-        extra_hash=_extra_hash(extra_params),
+        extra_params=extra_params,
     )