fix(kiro): estimate chat-file input tokens from every human turn, not a 500-char slice - #934

… invalidate cached history

decodeKiroChatFile estimated input tokens from pendingUserMessage - the last
human turn sliced to 500 chars - while output summed every bot char, so any
multi-turn session or final prompt over 500 chars under-reported input tokens
(and therefore costUSD) severalfold.

The estimate is now the sum of every human turn's full character count, with
the 500-char cap kept for the display userMessage only. That closes most of
the gap but does NOT reach parity with the modern-execution, CLI-session and
V2 arms: those count tool and system records as input - their code comments
state tool results are fed back to the model - while the chat arm still
counts only human records. Tool content demonstrably exists in the format
(the G2 fixture carries a tool record), so the chat arm still under-reports;
it just under-reports far less than before. The blast radius is the
chat-file arm alone: the IDE-file dispatcher routes any record carrying a
chat array plus metadata to decodeKiroChatFile, so this is chat-shaped Kiro
IDE files, not every Kiro prompt.

The identity-preamble exclusion now trims leading whitespace before its
startsWith match. Pre-fix, a near miss (a leading newline, a BOM, a wrapper)
was nearly harmless, because the preamble only mattered if it happened to be
the last human turn; post-fix, every unmatched system-injected human record
adds its FULL length to input, and preambles are large - a missed match is a
silent multi-thousand-token inflation on every affected session. Leading
whitespace tolerance is cheap (a genuine prompt never starts with whitespace
plus an identity tag) and the failure asymmetry favours exclusion: a false
negative inflates tokens, a false positive only skips a preamble. A renamed
preamble remains a residual risk, noted in the near-miss regression test.

Cached history is affected, which is what a user actually sees. session-cache
serves unchanged files without invoking the provider parser, so bump kiro's
PROVIDER_PARSE_VERSIONS fingerprint (ide-parsing-v1 -> v2) to force one
re-parse of every already-cached kiro session; without it the pre-fix token
and cost numbers would be served forever.

The daily rollup ALSO needs invalidating for this fix to be fully visible:
days finalized before the fix keep their pre-fix kiro cost in the daily
cache, and ensureCacheHydrated re-derives them only on a version bump, a
savings-config change, a timezone change, or an incomplete cache — the
session-cache re-parse alone leaves finalized day totals untouched. So this
commit bumps BOTH layers: the session-cache PROVIDER_PARSE_VERSIONS
fingerprint above forces the one re-parse of every already-cached kiro
session, and DAILY_CACHE_VERSION (15 -> 17, MIN_SUPPORTED_VERSION raised
with it; 16 is skipped because main already claimed it for the codex
structural-discovery fix, and claiming 16 here would load a main-built v16
cache as current and complete, so the invalidation would never fire) forces
the daily rollup's one-time re-derivation, so finalized day
totals are rebuilt under the corrected estimate. The re-derive reaches every
day whose kiro chat files still exist; sourceless days carry forward with
their pre-fix totals under the v14 NEVER-LOSE rule (a carry-forward, not a
refresh — nothing can reconstruct them once the files are gone).

Update the G2 parity golden: A1 was pinned at 125 tokens for a 3000-char
prompt (the 500-char slice / 4); the corrected value is 750 (3000 / 4), with
a comment marking 125 as a pre-fix value so it is not restored. 3000, 2400
and 1000+1000 are all exact multiples of four, so add G2b pinning the
estimator's rounding with an odd length (3001 chars -> 751 tokens; round and
floor would both give 750). Add a money-path regression test (2400-char
prompt -> 600 tokens, userMessage still 500-capped for display), a
multi-turn accumulation test (an identical resubmitted prompt counts again -
a real second model input; identity messages stay excluded), a near-miss
identity test (leading-newline and BOM preambles stay excluded), extend the
kiro cache-invalidation test to pin the v1 -> v2 fingerprint bump, and add a
daily-cache regression test seeding a complete pre-fix v15 cache (unchanged
savings hash and timezone, so nothing but the version bump can invalidate
it) and proving the bump forces the re-derive that lands the corrected kiro
cost — while the v15 file is never rewritten.