Hashline prefixes (LINE:HASH|content) in read/grep output exist solely to
support the hashline edit mode. Agents that don't have the edit tool
(e.g. explore, plan, reviewer) gain nothing from them — they just waste
tokens and add noise.
resolveFileDisplayMode now takes a session-like object with an optional
hasEditTool flag. When false, hashlines are suppressed regardless of
settings. ToolSession gains hasEditTool (set from toolNames in the SDK),
and AgentSession exposes it as a getter over the tool registry.