Send a message to a DSH session

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Adds substantial behavior beyond the annotations: the call blocks until the turn settles, one prompt per session at a time, agent_thought_chunk content is filtered out unless DSH_CODEX_INCLUDE_THOUGHTS is set, and DSH tool permission requests default to DENIED unless permission_policy is 'allow_once'. These are exactly the non-obvious traits an agent needs before invoking a mutating, potentially long-running call.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Four sentences, each carrying distinct information: action, concurrency constraint, return shape, and permission/thought defaults. The action is front-loaded and no sentence is filler or duplicated from the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Even without an output schema, the description summarizes the return payload (assistant text, tool-call summary, usage) and covers blocking behavior, concurrency, and permission defaults. For a 4-parameter mutation with full schema coverage and annotations, nothing material is left unexplained.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds consequence-level meaning by explaining what permission_policy actually governs (DSH tool permission requests default to deny, never auto-approved) and that permission is per-turn. That goes beyond the schema's 'How to answer DSH tool permission requests for this turn.'

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a concrete verb and resource ('Send one user text message to an existing session via ACP session/prompt') plus the synchronous settle semantics. This is unmistakably different from the sibling session-management tools (list/create/resume/cancel/close), which do not carry payloads into a turn.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Implies the prerequisite clearly ('existing session') and states an operational constraint ('Exactly one prompt may be in flight per session'), which tells the agent not to fire concurrent sends. It stops short of naming an explicit alternative or spelling out the create-then-send sequence, so it is strong context rather than a full routing rule.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.