fix(web): let the context meter see a compaction

The composer ring, percentage, and `~used / capacity` header read
`contextPressure.pressureTokens`, which moves only when a request reports
usage. Compaction reports none — compact-basic summarizes through a direct
`ctx.llm.stream()` call and appends only its own `compact/*` records plus the
replacement `user/message` — so the meter was frozen across the one action
taken to change it. Driving a real `compactNow` through the agent loop:

    BEFORE compact:  ring=4%  header=~4227/100000  rows=[18, 0, 4365]
    AFTER  compact:  ring=4%  header=~4227/100000  rows=[18, 0,  286]

The composition rows fell 93%; the ring did not move, and would not until an
entire further turn completed. The panel then contradicted itself by more than
an order of magnitude at exactly the moment a reader opens it.

`contextPressure` now also publishes `projectedTokens`: the provider sample
plus the heuristic repricing of everything the surface gained or lost since
that sample, clamped at zero, folded through the shared `surface-fold.ts`. The
sample is stamped before the same event joins the surface, so an
`assistant/message` anchors against the surface its own request carried. Only
the delta is estimated, so the figure stays provider-anchored — the estimator's
CJK and JSON-schema underpricing stays out of the occupancy number — while
reacting the moment content lands or a span is shadowed. Same run after:

    BEFORE compact:  ring=4%  header=~4323/100000  (pressure=4227, projected=4323)
    AFTER  compact:  ring=0%  header=~ 244/100000  (pressure=4227, projected= 244)

`contextOccupancy` prefers the projected figure and falls back to the bare
sample, so a projection restored from a pre-field checkpoint degrades to the
old behavior rather than disappearing. `stateVersion` moves to 3.

.agents/notes/implemented/feature/2026-08-05-composer-context-meter-breakdown.md

@@ -16,7 +16,7 @@ Three cooperating pieces, one per package boundary:
 
 `dsh-token-meter` extracts its pricing heuristic into `src/estimate.ts` and its positional surface fold into `src/surface-fold.ts` — both shared verbatim with the measurement service — and registers a third session projection, `contextBreakdown`, carrying `systemTokens` / `toolsTokens` / `messageTokens`. Envelope figures reprice last-wins on each `request/header` through `canonicalHeader`; the message figure replays `foldSurfaceTokens` over a per-node `{seq, tokens}` list, so it equals `measure().surfaceTokens` at every event boundary by construction and compaction shrinks it the way it shrinks the next request. The shared fold is total and allocation-fresh — it returns the next surface rather than mutating one — which keeps the service's validate-before-commit replay transaction intact: a throw leaves the replay cursor unmoved and the same malformed event fails identically on retry. A replace range absent from the folded surface throws: committed logs are surface-validated at append time, so an unresolvable range is log corruption, not a skippable event.
 
-`ui-conversation` moves context occupancy off the stats line (one home per fact) onto a composer-trailing `ContextMeter`: a 14px occupancy ring after the model seat fed by `contextPressure`, click-opening a panel that pairs the provider-exact percent and `~used / capacity` header with a 4px color-segmented bar and `~`-prefixed composition rows. The two vocabularies deliberately never reconcile — the ring, header, and bar length stay provider-exact while the heuristic shares only proportion the bar's colored segments and rows, each marked `~` because the fixed 4-chars-per-token heuristic systematically underprices CJK text and code. The header is one localized sentence (`context.aria`, shared with the ring's accessible name) split around its `{percent}` slot, so each locale owns the reading's position — English leads with it, Chinese trails it — while the reading keeps its own tone; a bar part whose width computes to zero is dropped rather than rendered, because `.segment`'s min-width would otherwise paint a filled sliver at 0% occupancy.
+`ui-conversation` moves context occupancy off the stats line (one home per fact) onto a composer-trailing `ContextMeter`: a 14px occupancy ring after the model seat fed by `contextPressure`, click-opening a panel that pairs the provider-exact percent and `~used / capacity` header with a 4px color-segmented bar and `~`-prefixed composition rows. The two vocabularies deliberately never reconcile — the heuristic shares only proportion the bar's colored segments and rows, each marked `~` because the fixed 4-chars-per-token heuristic systematically underprices CJK text and code. (The ring, header, and bar length were provider-exact as shipped here; they now read the provider-anchored `projectedTokens` instead, because the bare sample could not see a compaction — see [the meter's compaction blindness](../bug-fix/2026-08-05-context-meter-blind-to-compaction.md).) The header is one localized sentence (`context.aria`, shared with the ring's accessible name) split around its `{percent}` slot, so each locale owns the reading's position — English leads with it, Chinese trails it — while the reading keeps its own tone; a bar part whose width computes to zero is dropped rather than rendered, because `.segment`'s min-width would otherwise paint a filled sliver at 0% occupancy.
 
 ## Alternatives considered