fix(1102): require non-empty origin.id on create_* MCP tools

bug 1102 was created today with origin={kind:user, id:""} because
build_origin silently defaulted id to empty when the caller didn't pass
one — we couldn't tell who filed it. Bug 1088's origin field is useless
as audit if every caller can omit themselves.

Changes:
- build_origin (server/src/http/mcp/story_tools/mod.rs) now returns
  Result<String, String> and rejects missing/empty/whitespace-only id
  with an instructional error pointing at bug 1102 / story 1104.
- 5 create_* tool handlers (bug, spike, refactor, epic, story) now
  resolve origin BEFORE create_*_file so an attribution-less call
  leaves no half-state behind.
- 5 tool input schemas now advertise origin as a required object via
  a shared origin_schema() helper. The schema description gives every
  caller (coder agent, chat bot, user, system) a concrete example so
  the LLM populates the field correctly on first sight.
- Test fixtures pass origin = {kind:"test", id:"test-suite"}.

Story 1104 (signed actions) is the longer-term replacement; this is the
quick attribution win agreed for master ahead of that design work.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/http/mcp/tools_list/story_tools.rs

@@ -2,6 +2,31 @@
 
 use serde_json::{Value, json};
 
+/// JSON schema fragment for the `origin` argument required by every `create_*`
+/// tool (bug 1102).  The caller MUST identify itself — empty `id` is rejected
+/// server-side so every work item carries a usable provenance trail.
+fn origin_schema() -> Value {
+    json!({
+        "type": "object",
+        "description": "Required: identifies the calling actor so every work item carries provenance. Empty/missing id is rejected (bug 1102). Examples: { \"kind\": \"agent\", \"id\": \"coder-1@story=42\" }, { \"kind\": \"chat-bot\", \"id\": \"Timmy@!room:home.local\" }, { \"kind\": \"user\", \"id\": \"dave\" }.",
+        "properties": {
+            "kind": {
+                "type": "string",
+                "description": "One of: \"agent\" (LLM coder/mergemaster/qa), \"chat-bot\" (Timmy or other chat-routed bot), \"user\" (human via CLI/MCP), \"system\" (server-automation)."
+            },
+            "id": {
+                "type": "string",
+                "description": "Non-empty identifier of the caller. For agents include the story id (e.g. \"coder-1@story=42\"); for chat-bots include the room/session (e.g. \"Timmy@!room:home.local\"); for users the user id or short name."
+            },
+            "ts": {
+                "type": "number",
+                "description": "Optional unix-seconds timestamp. Defaults to the server's clock when absent."
+            }
+        },
+        "required": ["kind", "id"]
+    })
+}
+
 /// Returns tool schemas for story/work-item lifecycle management.
 pub(super) fn story_tools() -> Vec<Value> {
     vec![
@@ -37,9 +62,10 @@ pub(super) fn story_tools() -> Vec<Value> {
                     "commit": {
                         "type": "boolean",
                         "description": "If true, git-add and git-commit the new story file to the current branch"
-                    }
+                    },
+                    "origin": origin_schema()
                 },
-                "required": ["name", "acceptance_criteria"]
+                "required": ["name", "acceptance_criteria", "origin"]
             }
         }),
         json!({
@@ -282,9 +308,10 @@ pub(super) fn story_tools() -> Vec<Value> {
                         "items": { "type": "string" },
                         "minItems": 1,
                         "description": "List of acceptance criteria (at least one required)"
-                    }
+                    },
+                    "origin": origin_schema()
                 },
-                "required": ["name", "acceptance_criteria"]
+                "required": ["name", "acceptance_criteria", "origin"]
             }
         }),
         json!({
@@ -323,9 +350,10 @@ pub(super) fn story_tools() -> Vec<Value> {
                         "type": "array",
                         "items": { "type": "integer" },
                         "description": "Optional list of story numbers this bug depends on (e.g. [42, 43]). Persisted as depends_on in YAML front matter."
-                    }
+                    },
+                    "origin": origin_schema()
                 },
-                "required": ["name", "description", "steps_to_reproduce", "actual_result", "expected_result", "acceptance_criteria"]
+                "required": ["name", "description", "steps_to_reproduce", "actual_result", "expected_result", "acceptance_criteria", "origin"]
             }
         }),
         json!({
@@ -360,9 +388,10 @@ pub(super) fn story_tools() -> Vec<Value> {
                         "type": "array",
                         "items": { "type": "integer" },
                         "description": "Optional list of story numbers this refactor depends on (e.g. [42, 43]). Persisted as depends_on in YAML front matter."
-                    }
+                    },
+                    "origin": origin_schema()
                 },
-                "required": ["name", "acceptance_criteria"]
+                "required": ["name", "acceptance_criteria", "origin"]
             }
         }),
         json!({
@@ -399,9 +428,10 @@ pub(super) fn story_tools() -> Vec<Value> {
                         "type": "array",
                         "items": { "type": "string" },
                         "description": "Optional: list of high-level success criteria for the epic"
-                    }
+                    },
+                    "origin": origin_schema()
                 },
-                "required": ["name", "goal"]
+                "required": ["name", "goal", "origin"]
             }
         }),
         json!({