fix: read semantic sources safely (#284)

* fix: read semantic sources safely

* test: retarget reindex per-scope error case to a broken manifest

Reading a broken standalone source was made non-fatal in de1f1a8d (it is
surfaced for repair instead of throwing), so the reindex per-scope error
test no longer captured an error. Point it at a corrupt manifest shard,
which is the remaining fatal read failure the per-scope catch must
isolate, and assert the captured error names the offending file.

* fix(sl): decouple semantic-layer file names from warehouse naming rules

The in-file `name:` field is now the sole source identity; the filename is
a derived label that never participates in identity. This removes the
"Unsafe semantic-layer source name" failure class entirely: any warehouse
identifier (Snowflake's uppercase SIGNED_UP, EVENT$LOG, dotted names) can
be read, overlaid, edited, and deleted.

- New `source-files.ts`: one total filename derivation (safe lowercase
  names verbatim; otherwise slug + sha256-hash suffix, immune to
  case-insensitive-filesystem collisions) and one by-name file resolver.
- Reads resolve by name everywhere; the path-from-name fast path and
  `assertSafeSourceName` are gone.
- Writes resolve-then-write: rewrites land on the file that declares the
  name (human renames survive); new sources get a derived filename; a
  derived path occupied by a different source fails instead of clobbering.
- `readSourceFile` returns null for missing files instead of forcing every
  caller to launder IO errors; `deleteSource` distinguishes manifest-backed
  sources from not-found instead of silently succeeding.
- `sl_write_source` accepts verbatim warehouse identifiers (snake_case is
  now a recommendation for new sources) and rejects sourceName/source.name
  mismatches; `sl_edit_source` rejects name-changing edits.
- Ingest projection commits, gate-repair allowlists, and touched-source
  derivation use resolved paths / in-file names instead of interpolating
  `<connId>/<name>.yaml`.
- Collapsed the five parallel path derivations and duplicated path-token
  helpers onto the shared module; dropped dead service methods.

* fix(sl): resolve sources by declared name end-to-end and gate warehouse SQL with the parser-backed validator

- Key broken/renamed semantic-layer files by their recoverable in-file
  name (slSourceNameForFile) so mid-edit sources stay reachable under
  their real identity in reads, listings, and search
- Derive finalization touched sources from composed-source diffs and
  recover deleted files' declared names from the pre-change commit
  instead of parsing hash-derived filenames
- Resolve revert/rollback paths against history (listFilesAtCommit) so
  human-renamed files are restored where they lived at preHead
- Validate ingest sql_execution through the daemon's sqlglot
  validateReadOnly in the connection's dialect, sharing one
  driver-to-dialect map (sql-analysis/dialect.ts) across MCP and ingest
- Harden the local read-only SQL backstop: accept leading comments,
  reject smuggled second statements, and strip trailing
  semicolons/comments before row-limit wrapping

docs-site/content/docs/guides/writing-context.mdx

@@ -44,12 +44,17 @@ Use this order for most context changes:
 Semantic sources are YAML files for queryable tables or custom SQL. They define
 agent-facing measures, dimensions, segments, joins, and grain.
 
-Semantic source files live at:
+Semantic source files live under:
 
 ```text
-semantic-layer/<connection-id>/<source-name>.yaml
+semantic-layer/<connection-id>/
 ```
 
+The file's `name:` field is the source's identity — it carries the warehouse
+identifier verbatim, including case. The filename is a derived label: simple
+lowercase names get `<source-name>.yaml`, anything else gets a slugged
+filename. Renaming a file does not rename the source.
+
 ### Minimal source
 
 ```yaml
@@ -152,7 +157,7 @@ joins:
 
 | Field | Required | Description |
 |-------|----------|-------------|
-| `name` | Yes | Source identifier. Use lowercase words and underscores. |
+| `name` | Yes | Source identity (not the filename). When overlaying an ingested table, match the manifest identifier verbatim, including case (e.g. `SIGNED_UP`); for a new standalone source, lowercase words and underscores are recommended. |
 | `descriptions` | No | Description map keyed by source, such as `user`, `dbt`, or `ai`. |
 | `table` or `sql` | Yes | Database table or custom SQL expression. Use exactly one. |
 | `grain` | Yes | Columns that uniquely identify a row at the source grain. |