fix(compact): make config knobs explicit and flag two review smells

Address @tianyicui's minor-revision review on PR #110:

- Make every BasicCompactConfig knob required except `auto` (defaults
  true): there is no data yet to justify default thresholds/budgets, so
  a consumer states each value explicitly. Drop the DEFAULTS export and
  the constructor's `= {}` default; example cordis.yml, the compaction
  e2e, the README, and every test construction site now pass a complete
  config (tests route through a `cfg()` helper).
- Add a TODO on estimateContentTokens: char/4 is coarse; replace with a
  real tokenizer or post-response usage feedback in a follow-up.
- Add a TODO on the agent/pre-step `fullSystemPrompt` param flagging it
  as a smell on a generic per-step seam (compaction is its sole
  consumer); a `//` line comment so it stays out of the generated catalog.

packages/compact/compact-basic/src/index.ts

@@ -39,7 +39,7 @@ import type { BasicCompactConfig, ResolvedConfig } from './types.ts'
 import { resolveConfig } from './types.ts'
 
 export type { BasicCompactConfig, ResolvedConfig } from './types.ts'
-export { DEFAULTS, resolveConfig } from './types.ts'
+export { resolveConfig } from './types.ts'
 
 /** Per-block structural overhead for JSON framing / type tag. */
 const BLOCK_OVERHEAD = 4
@@ -155,10 +155,10 @@ function finishError(finish: FinishReason): Error | undefined {
 export class BasicCompactService extends CompactService {
   static inject = ['llm']
 
-  /** Resolved configuration (defaults applied). */
+  /** Resolved configuration (`auto` defaulted). */
   readonly config: ResolvedConfig
 
-  constructor(ctx: Context, config: BasicCompactConfig = {}) {
+  constructor(ctx: Context, config: BasicCompactConfig) {
     super(ctx)
     this.config = resolveConfig(config)
 
@@ -207,6 +207,9 @@ export class BasicCompactService extends CompactService {
 
   // ---- Token estimation (overridable hooks) ----
 
+  // TODO: char/4 is a coarse heuristic. Replace with an exact count — a real
+  // tokenizer, or the provider's post-response `usage` (input tokens) fed back
+  // as a correction — so threshold decisions match the model's actual budget.
   /**
    * Estimate the token count of content blocks — char/4 with per-block
    * overhead. Override in a subclass to plug in a real tokenizer.