Document prompt sessions and concurrency defaults

docs/internal/cli.md

@@ -89,9 +89,11 @@ handoff:
    profiles;
 4. materialize external or generated references and record redacted invocation
    and resolution provenance when debug capture is enabled;
-5. construct registries, the scheduled LLM client, prepared modules, and the
-   requested cache/checkpoint collaborators;
-6. read the source input and invoke the framework runner; and
+5. construct registries, the scheduled LLM client, and prepared modules;
+6. read the source input once, resolve its effective session from the explicit
+   override or resolved input module and raw bytes, then construct requested
+   checkpoint collaborators and invoke the framework runner with that same
+   value; and
 7. write the runner's logical output files only after a successful run, then
    complete the command report and user-facing result.
 
@@ -102,6 +104,13 @@ final command result. Detailed state lifecycle, resume handling, and physical
 path confinement are maintained in [Run State Internals](state.md) and
 [Operations](../operations.md).
 
+The CLI owns the versioned generated-session policy and resolves the sole
+effective value before checkpoint construction. It records that value in the
+final debug invocation summary when capture is enabled and passes it unchanged
+to checkpoint identity and `pipeline.RunInput`. The public flag and stability
+contract are defined by the [CLI reference](../cli.md#run); framework and LLM
+packages only transport the supplied value.
+
 For `run --json`, the CLI constructs and encodes its private run-result receipt
 after a successful runner result is available, before it publishes logical
 output files. It writes the prepared receipt to standard output only after