TurnResult: remove text field, simplify oneshot loop

- Remove TurnResult.text (was dead code - Agent::turn handles text internally)
- Simplify run_with_backend to just iterate over steps (Agent::turn loops
  for tool calls and handles empty responses internally)
- Change run/run_shared/run_forked_shared to return Result<(), String>
- Remove AgentResult.output field (no callers used it)
- Stub out legacy text-parsing code (audit, compare) that needs redesign
- Update digest.rs to not depend on text return
- Add level parameter to journal_new/journal_update for digest support

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/main.rs

@@ -466,36 +466,6 @@ enum AgentCmd {
         #[arg(long)]
         apply: bool,
     },
-    /// Mine conversation for experiential moments to journal
-    #[command(name = "experience-mine")]
-    ExperienceMine {
-        /// Path to JSONL transcript (default: most recent)
-        jsonl_path: Option<String>,
-    },
-    /// Extract atomic facts from conversation transcripts
-    #[command(name = "fact-mine")]
-    FactMine {
-        /// Path to JSONL transcript or directory (with --batch)
-        path: String,
-        /// Process all .jsonl files in directory
-        #[arg(long)]
-        batch: bool,
-        /// Show chunks without calling model
-        #[arg(long)]
-        dry_run: bool,
-        /// Write JSON to file (default: stdout)
-        #[arg(long, short)]
-        output: Option<String>,
-        /// Skip transcripts with fewer messages
-        #[arg(long, default_value_t = 10)]
-        min_messages: usize,
-    },
-    /// Extract facts from a transcript and store directly
-    #[command(name = "fact-mine-store")]
-    FactMineStore {
-        /// Path to JSONL transcript
-        path: String,
-    },
     /// Run a single agent by name
     Run {
         /// Agent name (e.g. observation, linker, distill)
@@ -526,19 +496,6 @@ enum AgentCmd {
         #[arg(long, default_value_t = 10)]
         count: usize,
     },
-    /// Evaluate agent quality by LLM-sorted ranking
-    #[command(name = "evaluate")]
-    Evaluate {
-        /// Number of pairwise matchups to run
-        #[arg(long, default_value_t = 30)]
-        matchups: usize,
-        /// Model to use for comparison (haiku or sonnet)
-        #[arg(long, default_value = "haiku")]
-        model: String,
-        /// Show example comparison prompt without calling LLM
-        #[arg(long)]
-        dry_run: bool,
-    },
 }
 
 #[derive(Subcommand)]
@@ -790,16 +747,9 @@ impl Run for AgentCmd {
                 => cli::agent::cmd_apply_consolidation(apply, report.as_deref()),
             Self::Digest { level }   => cmd_digest(level),
             Self::DigestLinks { apply } => cli::agent::cmd_digest_links(apply),
-            Self::ExperienceMine { .. }
-                => Err("experience-mine has been removed — use the observation agent instead.".into()),
-            Self::FactMine { path, batch, dry_run, output, min_messages }
-                => cli::agent::cmd_fact_mine(&path, batch, dry_run, output.as_deref(), min_messages),
-            Self::FactMineStore { path } => cli::agent::cmd_fact_mine_store(&path),
             Self::Run { agent, count, target, query, dry_run, local, state_dir }
                 => cli::agent::cmd_run_agent(&agent, count, &target, query.as_deref(), dry_run, local, state_dir.as_deref()),
             Self::ReplayQueue { count } => cli::agent::cmd_replay_queue(count),
-            Self::Evaluate { matchups, model, dry_run }
-                => cli::agent::cmd_evaluate_agents(matchups, &model, dry_run),
         }
     }
 }