fix: address ds-review-bot v7 findings on the merged image-input head

- gate model selection on steering-placement image carriers from enqueue
  until their steering/message event publishes; release the gate when an
  admission ends idle without publication (both behaviorally asserted)
- reject session.updateQueue edits carrying non-text blocks at the RPC
  boundary (queue edits cannot bypass image admission)
- extend the durable-directory walk past a first-created DSH_HOME to the
  deepest pre-existing ancestor
- strip Windows-style separators from attachment display names on POSIX
- verify attachment reads with a header-only probe (digest already proves
  the bytes decoded fully at admission); document the read path
- make SessionInputShell.addImages refusal observable and keep workspace
  transfers/composer intake from leaking refused drafts
- own ONE recursive image walk (dsh-llm contentHasImage) across apiproxy,
  pi-ai, compact-basic, and the DeepSeek text-only assertion
- drop the redundant canonical-base64 regex and the no-op role read
- move AttachmentId/AttachmentError out of types.ts (brand.ts/error.ts);
  document why AttachmentError does not extend HarnessError
- document the hard attachments inject in both consumer READMEs

docs/cordis-catalog/events.md

@@ -567,7 +567,7 @@ Waterfall around every streaming model call (retry, replay, routing). Bound to t
 
 Types: [GenerateOptions](../core-data-structures/core.md) · [LlmService](../core-data-structures/llm-streaming.md) · [StreamChunk](../core-data-structures/llm-streaming.md)
 
-Source: [`packages/llm/llm/src/index.ts:59`](../../packages/llm/llm/src/index.ts)
+Source: [`packages/llm/llm/src/index.ts:60`](../../packages/llm/llm/src/index.ts)
 
 ## `session/*`
 

docs/cordis-catalog/services.md

@@ -285,7 +285,7 @@ abstract readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment>
 
 Types: [ImageAttachmentRef](../core-data-structures/attachment.md) · [SaveImageAttachment](../core-data-structures/attachment.md) · [StoredImageAttachment](../core-data-structures/attachment.md)
 
-Source: [`packages/attachment/attachment/src/index.ts:28`](../../packages/attachment/attachment/src/index.ts)
+Source: [`packages/attachment/attachment/src/index.ts:29`](../../packages/attachment/attachment/src/index.ts)
 
 ## `ctx.bash` — `BashExecutor` (abstract seam)
 
@@ -852,7 +852,7 @@ stream(options: GenerateOptions): AsyncIterable<StreamChunk>
 
 Types: [GenerateOptions](../core-data-structures/core.md) · [LlmAdapter](../core-data-structures/llm-streaming.md) · [LlmCallConfig](../core-data-structures/core.md) · [LlmModelInfo](../core-data-structures/core.md) · [LlmProviderInfo](../core-data-structures/core.md) · [LlmResolvedModelInfo](../core-data-structures/core.md) · [PreparedLlmCall](../core-data-structures/llm-streaming.md) · [ResolvedRetryPolicy](../core-data-structures/llm-streaming.md) · [StreamChunk](../core-data-structures/llm-streaming.md)
 
-Source: [`packages/llm/llm/src/index.ts:192`](../../packages/llm/llm/src/index.ts)
+Source: [`packages/llm/llm/src/index.ts:193`](../../packages/llm/llm/src/index.ts)
 
 ## `ctx.permission` — `PermissionService`