# aish — Phase 8 Manifest

**Project:** aish — AI-augmented conversational shell
**Document:** Phase 8 Requirements, Architecture & Design Decisions
**Status:** Formulate (pre-analyze)
**Date:** 2026-05-16

PHASE0 is the locked substrate; PHASE1-7 are layered on top. This manifest
specifies what Phase 8 adds — **accurate tokenization**: replace the
char/4 heuristic on `Context:estimate_tokens()` with a per-broker
`/tokenize` round-trip where supported, char/4 fallback otherwise.

Resolves Q1 (`PHASE0.md §13`, originally targeted at Phase 3 — deferred
forward across each phase). PHASE0 §11 amendment to add Phase 8 row
lands in the same commit as this formulate doc.

---

## 1. Scope of Phase 8

Four pillars:

1. **Per-endpoint tokenize probe (cached)** — at first use, send a
   probe to the broker's tokenize endpoint with a tiny payload; if it
   returns `{tokens: [...]}` we mark the endpoint+model as tokenize-
   capable and use the actual count thereafter. If it 404s or errors,
   mark the slot as `tokenize_supported = false` and fall through to
   char/4 silently. Cached per `(endpoint, model)` for the session.

2. **`broker.token_count(model_cfg, text)`** — thin wrapper that
   returns an accurate token count when the (endpoint, model) is
   tokenize-capable, else the char/4 heuristic. Always returns a
   non-negative integer; never errors. The probe + fallback is
   transparent to callers.

3. **`Context:estimate_tokens()` widening** — currently char/4 over
   `system_prompt` + sum of `turn.content`s. The new shape accepts
   an optional `tokenize_fn` (callback) at `Context.new` time and uses
   it when present; falls back to char/4 when nil. `repl.lua` wires
   `tokenize_fn = function(text) return broker.token_count(active_cfg, text) end`.
   This means the active model's tokenizer is used for budgeting
   decisions, which matches the broker the next ask_ai will hit.

4. **`:cost detail` estimated-vs-actual column** — for each
   (model, category) slot in the accumulator, the actual
   `prompt_tokens` from broker usage is already stored. Add an
   estimated column computed via `broker.token_count` on the
   currently-buffered prompt-shape. Disagreement >10% surfaces in a
   tiny `~est=N` annotation so users can see when the heuristic
   diverges from reality. Display-only; no behavior change.

**Phase 8 is done when:**

- A long-running session with the local `qwen-coder-7b-snappy-8k`
  model evicts at the RIGHT moment (actual context fills the
  budget) rather than ~10% late per the baseline gap.
- `broker.token_count(local_cfg, "hello world")` returns 2 (matches
  the live tokenize result, not the char/4=2 coincidence — verify
  via `:cost detail` against multi-paragraph text).
- `broker.token_count(cloud_cfg, "hello world")` returns 2 (char/4
  fallback when /tokenize 404s, which it does for OpenRouter).
- Cached per-endpoint capability — the probe fires once per
  endpoint per session, not per call.
- Existing configs without `cfg.tokenize` behave like Phase 7 (zero
  behavior change unless opted in via `cfg.tokenize.use_endpoint = true`).
- `:cost detail` shows estimated-vs-actual where disagreement >10%,
  silent otherwise.

---

## 2. Technology Decisions (delta from Phase 7)

| Decision | Choice | Rationale |
|---|---|---|
| Tokenize endpoint path | `<endpoint>/tokenize` (NOT `<endpoint>/v1/tokenize`) | Per real probe against hossenfelder: `/v1/tokenize` returns 404; `/tokenize` returns `{tokens: [...]}`. This is the llama.cpp server convention. |
| Request body shape | `{"content": "<text>", "model": "<model>"}` | Local model echoed via `model`; llama.cpp ignores it but harmless. Probed shape works. |
| Capability detection | Per-call optimistic probe; on 404/non-200, cache `tokenize_supported[endpoint][model] = false` and never retry that session | One round-trip cost on first miss; zero on subsequent. Sessions are short enough that re-probe across restarts is fine. |
| Fallback heuristic | char/4 (Phase 0 §8 convention) | Established; underestimates ~10% on real code/prose per baseline B1, but acceptable when no better signal available. |
| `Context:estimate_tokens` calling convention | Optional `tokenize_fn` callback at Context.new; absent = char/4 (existing behavior) | Backward-compatible; no caller break. Opt-in via repl.lua. |
| Active-model tokenizer | repl.lua wires `tokenize_fn` against `active_cfg` (the currently active model), so eviction decisions match the broker the next call will hit | When the user `:model cloud` switches mid-session, subsequent estimates use cloud's tokenizer (which falls back to char/4 since OpenRouter has no /tokenize). |
| Caching strategy | Endpoint+model capability flag only; NOT per-text token-count cache | Token counts depend on text content; caching adds memory + correctness risk for marginal speed. Probe latency dominates only on first call per endpoint. |
| Per-text timeout cap | 2s for tokenize calls (much tighter than the model's normal timeout_ms) | Tokenize is a small, fast operation; if it doesn't respond in 2s, the endpoint is misbehaving. Bail to char/4. |
| `:cost detail` est-vs-actual | Show only when disagreement >10%; format `(prompt: 558 ~est=508 / completion: 80)` for the disagreement case, `(prompt: 558 / completion: 80)` otherwise | Always-on noise; suppress when heuristic is close. |
| New config key | `cfg.tokenize = { use_endpoint = true }` — default false until user opts in | Network round-trip cost; user-acknowledged behavior change. |

---

## 3. Module Changes

| File | State after Phase 7 | Phase 8 changes |
|---|---|---|
| `broker.lua` | `chat`, `chat_stream`, `build_request` (opts-widened in Phase 7) | New `M.token_count(model_cfg, text)`: tries `<endpoint>/tokenize` once per (endpoint, model); caches capability; returns int. New `M.tokenize_supported(model_cfg)` introspection helper for tests. |
| `context.lua` | `estimate_tokens()` char/4 sum over system_prompt + turn.contents | Widen to use `self.tokenize_fn(text)` if present; else char/4. New `tokenize_fn` field on Context (set at Context.new from opts). |
| `repl.lua` | wires Context.new with summarize_fn, hosts all metas | `tokenize_fn` wired into Context.new when `cfg.tokenize.use_endpoint = true`. `:cost detail` extended with est-vs-actual column. |
| `config.lua` | Phase 7 cost block example | Add commented-out `tokenize = { use_endpoint = true }` block. |
| `docs/PHASE0.md` | §11 lists phases 0-7 | Amendment: add Phase 8 row to §11. |

No new module files.

---

## 4. Pillar 1+2 — `broker.token_count(model_cfg, text)`

```lua
-- Per-endpoint capability cache (session-scoped local in broker.lua)
local _tokenize_capable = {}    -- [endpoint .. "/" .. model] = true | false

local function _cache_key(model_cfg)
    return (model_cfg.endpoint or "") .. "/" .. (model_cfg.model or "")
end

function M.token_count(model_cfg, text)
    text = text or ""
    if text == "" then return 0 end
    if not (model_cfg and model_cfg.endpoint) then
        return math.floor(#text / 4)   -- pure fallback
    end
    local key = _cache_key(model_cfg)
    local cap = _tokenize_capable[key]
    if cap == false then
        return math.floor(#text / 4)
    end
    -- cap == nil OR cap == true; try the endpoint.
    local url = model_cfg.endpoint:gsub("/+$", "") .. "/tokenize"
    local body = json.encode({ content = text, model = model_cfg.model })
    local out, status = curl.post(url, body,
        { "Content-Type: application/json" },
        2000)  -- 2s timeout
    if not (status == 200 and out) then
        _tokenize_capable[key] = false
        return math.floor(#text / 4)
    end
    local doc = json.decode(out)
    local toks = doc and doc.tokens
    if type(toks) ~= "table" then
        _tokenize_capable[key] = false
        return math.floor(#text / 4)
    end
    _tokenize_capable[key] = true
    return #toks
end

function M.tokenize_supported(model_cfg)
    if not model_cfg then return nil end
    return _tokenize_capable[_cache_key(model_cfg)]
end
```

Uses Phase 1's `ffi/curl.M.post` (blocking POST, returns body + status).

---

## 5. Pillar 3 — `Context:estimate_tokens` widening

```lua
function M.new(opts)
    ...
    return setmetatable({
        ...
        -- Phase 8: optional callback that returns an accurate token
        -- count for a given text. Set by repl.lua when cfg.tokenize.
        -- use_endpoint=true, calling broker.token_count(active_cfg, ...).
        -- nil = char/4 fallback (Phase 0 §8 behavior).
        tokenize_fn          = opts.tokenize_fn,
    }, Context)
end

function Context:estimate_tokens()
    if self.tokenize_fn then
        local n = self.tokenize_fn(self.system_prompt)
        for _, t in ipairs(self.turns) do
            n = n + self.tokenize_fn(t.content)
        end
        return n
    end
    -- char/4 fallback (existing behavior)
    local n = #self.system_prompt
    for _, t in ipairs(self.turns) do n = n + #t.content end
    return math.floor(n / 4)
end
```

Performance note: with N turns of average ~500 chars each, `estimate_tokens`
fires N tokenize round-trips. For N=40 turns × 50ms = 2s — too slow for
per-prompt eviction checks. **Mitigation**: per-turn token count cached
ON the turn dict (`turn._tokens`) the first time it's counted; only
re-tokenized if `turn._tokens` is nil. Set at append time when
tokenize_fn is present; otherwise lazily on first estimate.

---

## 6. Pillar 4 — `:cost detail` est-vs-actual

Current `:cost detail` (Phase 7) shows:

```
  anthropic/claude-haiku-4.5 main                 1 calls,    179 /      8 tokens, $0.000219
```

The `179 / 8` is `prompt_tokens / completion_tokens` from the actual
broker usage payload.

Phase 8 extension: for each slot, also compute an estimated count via
`broker.token_count(model_cfg_for_this_slot, ...)` over the
TURNS THAT CONTRIBUTED to this slot. But that's stateful and
expensive — simpler: show the SUM of `prompt_tokens` (actual) and
the SUM of `estimate_tokens()` (heuristic OR endpoint-based, depending
on what tokenize_fn is wired). If disagreement >10%, annotate.

Simplified format:

```
  anthropic/claude-haiku-4.5 main                 1 calls,    179 ~est=164 / 8 tokens, $0.000219
                                                                    ^^^^^^^^^^ shown when |actual-est|/actual > 0.10
```

The `~est=N` annotation only renders when the disagreement exceeds the
10% threshold. Silent otherwise.

---

## 7. UX Surface Summary

| Meta | Behavior change |
|---|---|
| `:cost detail` | Adds `~est=N` annotation per slot when heuristic disagreement >10% |
| (no new metas in v1) | |

| Config | Default | Effect |
|---|---|---|
| `cfg.tokenize.use_endpoint` | false | When true, repl.lua wires `tokenize_fn` so context budgeting uses real token counts |

The `cfg.tokenize` block being opt-in is conservative: enabling it
means every `Context:estimate_tokens()` call may hit the broker. For
local llama.cpp the cost is ~50ms; for cloud-only configurations there
IS no /tokenize endpoint so we silently fall through to char/4 (cached
after one probe). No surprise; document in config example.

---

## 8. Out of Scope (Phase 8)

- **Cost preflight enforcement** — option 2 of the Phase 7 §12
  candidates. The tokenize work here is a PREREQUISITE for accurate
  preflight cost estimation, but the enforcement layer itself
  (cap_at_dollars that REFUSES the call) is its own surface — defer
  to a separate phase.
- **Cross-session cost rollup** — option 1 of Phase 7 §12 candidates.
  Independent of tokenization.
- **Streaming tokenize** — some servers expose streaming tokenize
  endpoints for partial-prompt token counts during generation. Out
  of scope here; we use the blocking /tokenize for batch estimates.
- **Multi-tokenizer support** (e.g. tiktoken for OpenAI compat,
  sentencepiece for HuggingFace) — would require vendoring a C library
  (violates PHASE0 §3) or shelling out to python. Endpoint-based is
  the only substrate-compliant option for accuracy beyond char/4.
- **Tokenization for `:cost detail` rows that span multiple turns**
  — the actual `prompt_tokens` in the accumulator slot is the sum
  ACROSS calls; the estimate for comparison should be over the
  CURRENT ctx content. Show the per-call comparison only.

---

## 9. Risks

| Risk | Mitigation |
|---|---|
| `/tokenize` 404 silently cached as `tokenize_supported = false` for a typo'd endpoint config | Per-session cache; restart re-probes. Acceptable. |
| Tokenize round-trip on every prompt eviction check adds 50ms × N turns latency | `turn._tokens` per-turn cache set at append-time; only re-tokenize on cache miss. |
| Hossenfelder proxy may forward `/tokenize` differently than direct llama.cpp (e.g., adds `/v1/` prefix expected) | B1 confirms `/tokenize` works against hossenfelder; other proxies untested but the design degrades gracefully (char/4 fallback). |
| Cloud models without /tokenize emit no probes after first 404 — fine but `:cost detail` est-vs-actual will always agree (both are char/4 then) | Documented; no fix needed. Display annotation hides when est=actual exactly OR within 10%. |
| `Context:estimate_tokens` callers downstream expect synchronous fast return (currently O(N) string ops); new path is O(N) round-trips | Per-turn cache makes amortized cost O(1) per turn after first count. |
| Endpoint URL handling — currently `endpoint .. "/v1/chat/completions"` is hardcoded; tokenize uses `endpoint .. "/tokenize"` (no /v1) — asymmetric | Document the asymmetry inline; the llama.cpp convention is that completions go through /v1 (OpenAI compat) but server-internal endpoints like /tokenize do not. |

---

## 10. Open Questions (Phase 8)

| # | Question | Impact | Resolution target |
|---|---|---|---|
| Q-T1 | Should the per-turn `_tokens` cache survive across `:reset`? `:reset` clears `turns` anyway, so the cache dies with them. But if turns get appended again, do we re-tokenize from scratch? | Cache lifecycle | Analyze (probably trivially yes — new turns get new cache entries) |
| Q-T2 | When the active model changes (`:model cloud`), should the `tokenize_fn` re-bind to the new model's tokenizer? The wiring is set once at Context.new time. | Eviction accuracy after `:model` switch | Analyze (the lambda captures `active_cfg` upval — Lua's closure semantics resolve at call time, so YES it follows :model switches naturally) |
| Q-T3 | Should the probe respect `cfg.tokenize.use_endpoint = false` and skip even the probe? Or always probe and just not USE the result if disabled? | Network behavior with config opt-out | Analyze (skip the probe entirely — opt-out means opt-out) |
| Q-T4 | What's the actual round-trip latency for `/tokenize` against the live broker for typical aish turn sizes (~500 chars)? | Performance model | Baseline |
| Q-T5 | Does hossenfelder's `/tokenize` accept the `model` field, or does it use whichever model is currently loaded? | Multi-model accuracy | Baseline |
| Q-T6 | Should `broker.token_count` also accept a TOOLS-array param so estimates include tool-schema tokens (which the chat_completion sends)? | Eviction accuracy with MCP tools | Analyze |

---

## 11. Phase 8 → Phase 9+ Out-of-band

Candidate follow-ups (non-binding):

- **Phase 9**: cost preflight enforcement (Phase 7 §12 option 2) —
  uses Phase 8's accurate token counts to refuse calls that would
  cross `cap_at_dollars`. The accuracy work here is the foundation.
- **Cross-session cost rollup** (Phase 7 §12 option 1) — independent;
  could land in parallel.
- **Phase X**: project-local config overlay (`.aish.lua`) — was the
  alternative scope to Phase 7's cost work. Still valuable but
  independent of any current line.

Phase 8 itself is self-contained — no upstream dependencies.