feat: comprehensive logging across parser, app, persistence, runtime (X1)

Completes the X1 full sweep started in a8ad0c6 (db.rs). Closes X1 -> [x].

- persistence/mod.rs: debug! on every yaml/CSV/history write -- the
  silent-failure-prone disk paths (write_schema, write_table_data incl.
  the empty->delete branch, append_history/_failure).
- runtime.rs: debug! on execute_command_typed dispatch (one per executed
  command, complements the db.rs executor logs).
- app.rs: debug! on submit (route + submission mode), dispatch_app_command,
  and the ADR-0044 diagram-vs-prose render-mode choice.
- dsl/parser.rs: trace! on parse begin/outcome at the parse_command_inner
  choke point -- trace, not debug, because the live overlay/completion
  re-parse per keystroke (hot path).
- logging.rs: documented level discipline (error/warn/info/debug/trace) so
  the convention survives across sessions.

Levels verified end-to-end through the real worker thread + logging::init.
~75 -> 135 tracing sites total. Tests: 2207 pass / 0 fail / 1 ignored.
Clippy clean.

src/app.rs

@@ -1311,6 +1311,13 @@ impl App {
             return Vec::new();
         }
 
+        debug!(
+            persistent_mode = ?self.mode,
+            submission_mode = ?submission_mode,
+            len = effective_input.len(),
+            "submit"
+        );
+
         // Parse-first: app-level commands and DSL commands now
         // share the chumsky parser (per the round-5 refactor).
         // App commands work in both modes — they're not gated by
@@ -1342,6 +1349,7 @@ impl App {
         source: &str,
     ) -> Vec<Action> {
         use crate::dsl::{AppCommand, MessagesValue, ModeValue};
+        debug!(command = ?cmd, "dispatch app command");
         match cmd {
             AppCommand::Quit => vec![Action::Quit],
             AppCommand::Help { topic } => {
@@ -1700,6 +1708,7 @@ impl App {
                     | Command::AddRelationship { .. }
                     | Command::DropRelationship { .. }
             ) {
+                debug!(verb = command.verb(), width = self.last_output_width, "render: relationship diagrams (ADR-0044)");
                 for line in crate::output_render::render_structure_with_diagrams(
                     desc,
                     self.last_output_width,

src/dsl/parser.rs

@@ -12,6 +12,8 @@
 //! synthetic "unknown command" error when the input's first
 //! identifier-shape token isn't a registered entry word.
 
+use tracing::trace;
+
 use crate::dsl::command::Command;
 use crate::mode::Mode;
 
@@ -150,13 +152,27 @@ fn parse_command_inner(
     schema: Option<&crate::completion::SchemaCache>,
     mode: Mode,
 ) -> Result<Command, ParseError> {
+    // `trace`, not `debug`: parsing is a hot path — the live overlay /
+    // completion (completion.rs) re-parse per keystroke, probing
+    // candidates in a loop, so a per-parse `debug` line would flood. The
+    // executed-command story lives at `debug` in db.rs (one per submit).
+    trace!(
+        len = input.len(),
+        mode = ?mode,
+        schema_aware = schema.is_some(),
+        "parse: begin"
+    );
     if input.trim().is_empty() {
+        trace!("parse: empty input");
         return Err(ParseError::Empty);
     }
-    if let Some(result) = try_walker_route(input, schema, mode) {
-        return result;
+    let result =
+        try_walker_route(input, schema, mode).unwrap_or_else(|| Err(unknown_command_error(input)));
+    match &result {
+        Ok(cmd) => trace!(command = cmd.verb(), "parse: ok"),
+        Err(e) => trace!(error = %e, "parse: rejected"),
     }
-    Err(unknown_command_error(input))
+    result
 }
 
 /// Synthetic ParseError for inputs whose first identifier-shape

src/logging.rs

@@ -6,6 +6,38 @@
 //! environment variable; if neither is set we default to
 //! `~/.rdbms-playground/playground.log` and create directories as
 //! needed.
+//!
+//! ## Level conventions (X1 — `requirements.md`)
+//!
+//! Instrumentation across the tree follows a consistent level
+//! discipline so the default `info` filter stays quiet and
+//! `RDBMS_PLAYGROUND_LOG=debug` (or `=trace`) is a rich, layered
+//! diagnostic stream. The env filter (`RDBMS_PLAYGROUND_LOG`,
+//! full `EnvFilter` syntax) controls this independently of the
+//! file path above; the default is `info`.
+//!
+//! - **`error!`** — unrecoverable failure (fatal persistence, a
+//!   panic-equivalent). The process is going down or a command is
+//!   hard-failing.
+//! - **`warn!`** — recoverable failure or a fallback taken (a
+//!   snapshot couldn't be staged, a `PRAGMA` couldn't be restored,
+//!   an integrity check rolled a rebuild back).
+//! - **`info!`** — low-volume lifecycle, visible by default: db
+//!   worker start/exit, project create/open, "logging initialised".
+//! - **`debug!`** — the bulk of instrumentation, one line per
+//!   *executed* command and the decision points within it (executor
+//!   entry with key params, autofill/cascade summaries, the
+//!   rebuild-table primitive, persistence writes, render-mode
+//!   choice). Off by default.
+//! - **`trace!`** — hot paths only: per-keystroke parsing
+//!   (`dsl::parser`), per-key input handling (`app`), per-refresh
+//!   table reads. A firehose; never on except when debugging that
+//!   specific layer.
+//!
+//! Rule of thumb for new code: a loop logs a single summary count,
+//! never per-iteration at `debug`/`info`. Logs are developer-facing,
+//! so naming the engine (SQLite/PRAGMA) is fine here even though the
+//! "no engine name" rule (ADR-0002) forbids it in user-facing strings.
 
 use std::fs::{File, OpenOptions, create_dir_all};
 use std::path::{Path, PathBuf};

src/persistence/mod.rs

@@ -19,6 +19,8 @@ use std::fs;
 use std::io::Write as _;
 use std::path::{Path, PathBuf};
 
+use tracing::debug;
+
 use crate::dsl::action::ReferentialAction;
 use crate::dsl::types::Type;
 use crate::mode::Mode;
@@ -338,6 +340,7 @@ impl Persistence {
     /// renames over the destination.
     pub fn write_schema(&self, schema: &SchemaSnapshot) -> Result<(), PersistenceError> {
         let body = yaml::serialize_schema(schema);
+        debug!(bytes = body.len(), "persist: write project.yaml (atomic)");
         atomic_write(&self.project_path.join(PROJECT_YAML), body.as_bytes())
     }
 
@@ -355,8 +358,10 @@ impl Persistence {
     /// with files they didn't ask for.
     pub fn write_table_data(&self, table: &TableSnapshot) -> Result<(), PersistenceError> {
         if table.rows.is_empty() {
+            debug!(table = %table.name, "persist: table empty -> removing CSV (no data, no CSV)");
             return self.delete_table_data(&table.name);
         }
+        debug!(table = %table.name, rows = table.rows.len(), "persist: write data/<table>.csv (atomic)");
         let data_dir = self.project_path.join(DATA_DIR);
         fs::create_dir_all(&data_dir).map_err(|source| PersistenceError::Io {
             operation: "create",
@@ -394,6 +399,7 @@ impl Persistence {
     pub fn append_history(&self, command_text: &str) -> Result<(), PersistenceError> {
         let path = self.project_path.join(HISTORY_LOG);
         let line = history::format_record(command_text, history::utc_iso8601_now());
+        debug!(len = command_text.len(), "persist: append ok record to history.log");
         history::append(&path, &line)
     }
 
@@ -411,6 +417,7 @@ impl Persistence {
             history::utc_iso8601_now(),
             history::STATUS_ERR,
         );
+        debug!(len = command_text.len(), "persist: append err record to history.log");
         history::append(&path, &line)
     }
 

src/runtime.rs

@@ -2531,6 +2531,7 @@ async fn execute_command_typed(
     command: Command,
     source: String,
 ) -> Result<CommandOutcome, DbError> {
+    debug!(verb = command.verb(), "execute command (routing to worker)");
     let src = Some(source);
     match command {
         Command::CreateTable {