fix(project): name the project a memory belongs to, and refuse to guess it

CHANGELOG.md

@@ -6,6 +6,7 @@ All notable changes to MeMesh are documented here.
 
 ### Fixed
 
+- `learn` can now be told which project a lesson belongs to (#527): the MCP tool and `POST /v1/learn` take an optional `project`, and `memesh learn` takes `--project`. Without one, the MCP tool and `memesh learn` still use the project of the process's working directory, as `task_state` does; `POST /v1/learn` now requires `project` and answers 400 (storing nothing) when it is missing, instead of filing the lesson under the directory `memesh serve` was started in. An empty project, or one written as a path (`/Users/me/proj`, `C:\proj`, `a/b`, `./foo`, `../foo`, `~/foo`), is now refused with an error naming the field by `learn`, `task_state`, `briefing`, `memesh learn`, `memesh task`, `memesh briefing` and `memesh import --notes`; a bare name such as `.ssh` is still accepted, and a project you pass is stored exactly as you wrote it. The read routes `GET /v1/task-state` and `GET /v1/briefing-index` still read a project key exactly as sent, so a legacy path-shaped key already in the database stays readable; they refuse a blank or over-long one, and `learn`, `task_state` and `briefing` accept no path (messaging and `kg rename-project` project rules are unchanged). The PreCompact hook no longer uses its own working directory when the payload has no usable `cwd`, and no longer writes payloads without a usable `session_id` into one shared `pre-compact-unknown` memory: a missing, blank or non-text `cwd` or `session_id` makes it skip and record the reason. `briefing`, like `learn` and `task_state`, now looks a project up exactly as written (no trimming, no Unicode normalising), so a lesson stored under a padded or accented project name shows in that project's briefing. When the MCP server's working directory is the directory it runs from (Codex starts a plugin's MCP server in the plugin root, so the working directory is not the user's workspace; a workspace is not affected, even when it is another MeMesh checkout; a server run from the very checkout it is started in, such as `claude --plugin-dir <checkout>` or `npm link`, counts as its own directory), `learn`, `task_state` and `briefing` without a `project` are refused with a one-line error asking for the project from the SessionStart briefing, instead of filing under the plugin directory's project. Memories already stored under a path-shaped project tag are left as they are.
 - A message sent through the MCP `message` tool keeps every `null` in its JSON payload. Before, the MCP boundary removed each null-valued key at any depth of the payload while `send` still reported success, so the recipient got different data than the CLI or HTTP would have stored (#517). A null-valued top-level tool parameter still means "left blank", except `payload`, whose null is a value (#553).
 - The MCP `message` tool accepts `payload: null` on `send`, as its schema and the HTTP API already did; it was refused with `payload: Invalid input` (#553).
 

dist/core/agent-scope-id.d.ts

@@ -4,6 +4,7 @@ export declare function canonicalAgentScopeId(value: string): string;
 export declare function isFilesystemPathScopeId(value: string): boolean;
 export declare function lastPathSegment(value: string): string | null;
 export declare function agentScopeIdRejection(field: string, value: string): string | null;
+export declare function projectScopeRejection(value: string): string | null;
 export declare const AGENT_MESSAGE_SCOPE_COLUMNS: ReadonlyArray<{
     readonly table: string;
     readonly columns: readonly string[];